Pyrite in Silurian graptolites from Bornholm, Denmark

Pyrite is present in many horizons in dark grey graptolite-rich shales of Llandovery-early Wenlock age on the island of Bornholm, Denmark. The pyrite usually occurs as internal moulds of the graptolites, but rarely on the outside of the periderm. Occasionally the internal pyrite protrudes from the apertures of the rhabdosomes. Investigations using reflected light and scanning electron microscopy have shown that the internal pyrite is texturally variable. The abundance of the framboids is variable, ranging from thin linings on the inner side of the periderm to nearly complete infills of the graptolite colony. The pyrite also occurs as densely packed microcrystals and as larger euhedral crystals in all transitions from individual crystals, often developed on the surfaces of the framboids. to compact aggregations. Some of the pyritized graptolites have central cavities in the rhabdosomal linings. Within the cavities there are striking stalactite-like forms of pyrite suspended from the roof of the periderm. Some specimens have late infillings by calcite in the central part of the tubes. Most of the internal pyrite must have been formed very early during the taphonomic processes operating on the graptolites, pre-dating the compaction of the sediment. The framboids were first precipitated, followed by the aggregated euhedral pyrite. It is debatable whether the tubes of the graptolites were fluid-filled or partially gas-filled when the stalactites were formed; the latter is the more likely. The beds with fully pyritized graptolites might represent an episodic increase of sedimentation rate and oxygen content of bottom waters. □ Pyrite, Silurian, graptolites, Bornholm, stalactites, early diagenesis.     

The ultrastructure of the Crustoidea and the evolution of graptolite skeletal tissues

The Crustoidea are important in discussions of graptolite origins, because they represent a morphoecological type intermediate between the Rhabdopleurida and the Dendroidea. TEM and SEM studies of their rhabdosomes provide new data on the structural variation displayed by the graptolite periderm. Since the crustoid fusellar fabric does not differ markedly from the fuseller fabric of other graptolites and is dissimilar to that of pterobranchs, it is supposed that the fundamental graptolite fibril pattern was attained at the crustoid stage of graptolite evolution. The crustoid cortex is made of paracortex (the multiple deposition of sheets separated by an intersheet material in the form of condensed meshwork of fibrous material) and of pseudocortex (the accumulation of sheets and intersheet material devoid of fibrous character). The presence of sporadically genuine cortex is noted. Presumably the mechanisms of cortical fibrilogenesis were attained at the crustoid stage, but only in an incipient and incomplete form. Modes of periderm corticization arc discussed. Sheets, common elements in secondary deposits of pterobranchs and graptolites, arc compared, but some problems still remain unclear. ?Crustoidea, Pterobranchia, phytogeny, ultrastructure, cortex, morphogenesis, homology.     

Decay and composition of the hemichordate Rhabdopleura: implications for the taphonomy of graptolites

Although the graptolites lacked biomineralised tissue, their skeletons are abundantly preserved in deeper-water mudstones. Decay experiments and observations on the closely related living hemichordate Rhabdopleura demonstrate that the periderm and stolon are highly resistant to decay, remaining intact for months, whereas the zooids are unrecognizable within days. The extreme rarity of the preservation of traces of the zooids in graptoloids reflects their planktic lifestyle; the zooids had normally decayed before burial. Curie-point-gas-chromatography (Py-GC) and Curie-point-gas-chromatography-mass spectrometry (Py-GC-MS) of the periderm of Rhabdopleura confirms that proteinaceous organic matter is a major constituent. Ultrastructurally preserved graptolite periderm (Ordovician, Oklahoma; Silurian, Arctic Canada), on the other hand, is a highly altered kerogen-like substance rich in aliphatic biomacromolecules. The composition of the preserved graptolite periderm reflects diagenetic replacement by components probably mainly derived from algal cell walls.     

PALAEOECOLOGY OF THE GRAPTOLITHINA, AN EXTINCT CLASS OF THE PHYLUM HEMICHORDATA

1. Whatever heirarchical system of classifying graptolites is adopted, perhaps even raising them to the rank of phylum, the hemichordates including Rhabdopleura and Cephalodiscus remain their closest relatives. 2. Benthonic graptolites preceded and outlasted the planktonic graptolites which exhibited spectacular morphological changes related to a change to a holoplanktonic mode of life and a probable hermaphroditism. 3. The resorption of the narrow-end of the larval skeleton (prosicular cauda) enabled the construction by an outer layer of secreting tissue (extrathecal tissue) of a hollow nema, the dark hollow rod which supported gas-filled tissue and which in turn conferred buoyancy on the colony. 4. The nema provided access to the exterior of the colony for extrathecal tissue which began to strengthen the outside of the prosicular and metasicular parts of the larval skeleton with laminated cortical deposits before the first non-sicular individual of the colony was budded. 5. Attachment of the larval stage in those graptolites having a basal disc or ‘roots’ was by the first-formed extrathecal tissue through a resorbed cauda. 6. Initial attachment of the larval stage in certain encrusting graptolites such as Idiotubus may have been by a larval individual lacking any scleroprotein periderm as a skeletal sheath. 7. After initial attachment the extrathecal tissue continued to secrete additional layers of cortical tissue mostly for the purposes of strengthening the colony. 8. Feeding in graptolites was by ciliated lophophore often positioned so as to take maximum advantage of currents flowing from the dorsal to the ventral side of the colony, for example in Dictyonema and Monograptus. 9. The main function of the nema, particularly of those nemata bearing vanes, was as a support for vacuolated tissue which imparted a holoplanktonic mode of life to planktonic (sensu Zato) graptolites. 10. Attachment of colonies (rhabdosomes) as groups of colonies (synrhabdosomes) was by the extrathecal tissue issuing from the tips of the nemata: such associations were probably sexual rather than for reasons of buoyancy. 11. Attachment of planktonic graptolites to floating algal fronds is an unnecessary hypothesis. Although an undoubted occurrence of graptolites in rocks containing large quantities of carbonaceous matter is beyond dispute, the plant or animal nature of this material has never been established. A symbiotic relationship of planktonic graptolites with a marine, formless alga, perhaps involving the extrathecal tissue, remains a possibility. 12. Although different species may have lived at different depths, the full vertical range of the holoplanktonic graptolites was probably small. The evidence advanced for depth zonation is considered inadequate. 13. Planktonic graptolites were essentially tropical to temperate in distribution with the bulk of the species and individuals in the former environment. 14. Automobility of graptolite rhabdosomes was an unlikely mechanism and does not readily account for the morphology and distribution of the graptolites. 15. Most planktonic graptolites were suspended beneath a nema coated in extrathecal, vacuolated (gas-filled) tissue: changes of position in the water were by passive response to ocean currents. 16. The nature of the graptolite zooid is considered unsolved, although it may have been essentially like that of the extant Rhabdopleura in having paired lophophores. 17. It is possible that a modified pre-oral lobe was capable of secreting both fusellar (inner) and cortical (outer) layers of the periderm. 18. The extrathecal tissue itself would in that case have been derived both from the nemal tube and the thecal individuals.     

The position of graptolites within Lower Palaeozoic planktic ecosystems

An integrated approach has been used to assess the palaeoecology of graptolites, both as a discrete group and as a part of the biota present within Ordovician and Silurian planktic realms. Study of the functional morphology of graptolites and comparisons with Recent ecological analogues demonstrates that graptolites most probably filled a variety of niches as primary consumers, with modes of life related to the colony morphotype. Graptolite coloniality was extremely ordered, lacking any close morphological analogues in Recent faunas. To obtain maximum functional efficiency, graptolites would have needed varying degrees of coordinated automobility. A change in lifestyle related to ontogenetic changes was prevalent within many graptolite groups. Differing lifestyle was reflected by differing reproductive strategies, with synrhabdosomes most likely being a method for rapid asexual reproduction. Direct evidence in the form of graptolithophage 'coprolitic' bodies, as well as indirect evidence in the form of probable defensive adaptations, indicate that graptolites comprised a food item for a variety of predators. Graptolites were also hosts to a variety of parasitic organisms and provided an important nutrient source for scavenging organisms. □ Feeding, graptolites, hydrodynamics, ontogeny, parasitism, palaeoecology, plankton, predation.     

ANATOMY OF SOME LEAF GALLS OF ROSA WOODSII (ROSACEAE)

Infection of Rosa woodsii by some members of the order Hymenoptera results in neoplasmic outgrowths on the leaves. One type of outgrowth produces a spherical swelling (leaf gall) while the other has extensive hair-like proliferations (hairy gall). The anatomy and ultrastructure of these galls were examined by light microscopy and transmission electron microscopy. The leaf gall cells were considerably larger than normal cells, lacked well-developed chloroplasts and were loosely arranged with prominent intercellular spaces. Vascular bundles were scattered throughout the gall tissue. The upper three cell layers of the leaf gall tissue resembles a periderm, having many suberin lamellae. The suberin lamellae were often traversed by pores which may represent incomplete plasmodesmata. Phenolic compounds were commonly seen both in the normal and gall cells. A layer of internal cells of the hairy galls have remarkably thickened cell walls, presumably due to the deposition of cellulosic substances. Unlike leaf galls, the epidermal cells of the hairy galls were not heavily cuticularized and no periderm was found. The hair-like outgrowths present on the outer surface of these galls had a central vascular bundle. The epidermis of the outgrowths also had thickened cell walls, and trichomes occurred on the outer surface. The structural modifications brought about by the insect invasion in these two galls are compared and their roles in gall formation are discussed.     

Collagen in the pterobranch coenecium and the problem of graptolite affinities

Amino-acid analysis of the extracellular skeleton (coenecium) of two pterobranchs (Hemichordata) Rhabdopleura normani and Cephalodiscus (C.) hodgsoni shows that both contain considerable quantities of collagenous material with relatively high hydroxyproline and low hydroxylysine levels. The appearance of the fibrous material in the skeleton of pterobranchs, although collagenous, differs from standard EM characteristics of collagen. The identification of the collagenous nature of the pterobranch skeleton with the presumed presence of collagen-like material in the periderm of fossil graptolites, taken in conjunction with other data, supports the hypothesis that both groups may be closely related phylogenetically.     

Histological analysis of the maturation of native and wound periderm in potato (Solanum tuberosum L.) Tuber

Maturation of potato (Solanum tuberosum L.) tuber native and wound periderm and development of resistance to periderm abrasion were investigated utilizing cytological and histochemical techniques. Both native and wound periderm consist of three different tissues: phellem, phellogen and phelloderm. It was previously determined that the phellogen walls of immature native periderm are thin and prone to fracture during harvest, leading to periderm abrasion (excoriation). Phellogen walls thicken and become less susceptible to fracture upon maturation of the periderm, leading to resistance to excoriation. We now demonstrate that phellogen cells of immature wound periderm also have thin radial walls and that wound periderm abrasion is due to fracture of these walls. Maturation of the wound periderm is also associated with an increase in the thickness of the phellogen radial walls. Histological analysis with ruthenium red and hydroxylamine-FeCI2, which stain unesterified and highly methyl-esterified pectins, respectively, indicates that the phellogen cell walls of native and wound periderm differ significantly regardless of the stage of maturity. Results obtained by staining with ruthenium red and hydroxylamine-FeCI2 imply that phellogen cell walls of immature native periderm contain methyl-esterified pectin, but are lacking in unesterified (acidic) pectins. Maturation of native periderm is accompanied by an apparent increase in unesterified pectins in the walls of phellogen cells, which may allow for the strengthening of phellogen cell walls via calcium pectate formation. Histological staining of the phellogen walls of wound periderm, on the other hand, implies that these walls are deficient in pectins. Moreover, maturation of wound periderm is not accompanied by an increase in unesterified pectins in these walls. Since peroxidase is known to catalyse the cross-linking of cell wall polymers, we stained native and wound periderm for the presence of peroxidase utilizing guaiacol as a substrate. Peroxidase staining was strong in the phellogen walls of both immature and mature native periderm and we could not detect any differences in staining between them. Peroxidase staining was weak in the phellogen walls of immature wound periderm and was not detectably different in mature wound periderm. Peroxidase data imply that there are distinct differences between native and wound periderm, though our data do not indicate that changes in peroxidase activity are involved in the development of resistance to periderm abrasion that occurs upon maturation of the periderm. However, we cannot rule out the involvement in this process of peroxidase isozymes that have low affinity for the substrates utilized here.     

Feinstrukturen und Verwandtschaftsbeziehungen der Graptolithen

Pterobranchs and graptolites exhibit essentially the same skeletal structure, namely a primary skeleton composed of regularly stacked bands and a later thickening made up of irregulary arranged, thinner elements. Both parts of the skeleton were most likely secreted via the individuals' cephalic discs. The most notable structural difference between the pterobranchs and graptolites can be seen in the secondary skeletal layers. In the graptolites it is made up of closely packed parallel fibers. The long distal thread (nema) of the planktonic graptolites is constructed and probably also secreted in a manner similar to that in which the skeleton is formed. Some sessile graptolites have more in common with recent pterobranchs than “normal” graptolites. The Crustoidea seem to be particulary well suited as model for the transition from pterobranch to graptolite structure. The minute structures of various pterobranchs and graptolites are depicted here, arranged approximately according to their probable evolution.     

A feruloyl transferase involved in the biosynthesis of suberin and suberin‐associated wax is required for maturation and sealing properties of potato periderm

Suberin and waxes embedded in the suberin polymer are key compounds in the control of transpiration in the tuber periderm of potato (Solanum tuberosum). Suberin is a cell‐wall biopolymer with aliphatic and aromatic domains. The aliphatic suberin consists of a fatty acid polyester with esterified ferulic acid, which is thought to play an important role in cross‐linking to the aromatic domain. In potato, ferulic acid esters are also the main components of periderm wax. How these ferulate esters contribute to the periderm water barrier remains unknown. Here we report on a potato gene encoding a fatty ω‐hydroxyacid/fatty alcohol hydroxycinnamoyl transferase (FHT), and study its molecular and physiological relevance in the tuber periderm by means of a reverse genetic approach. In FHT RNAi periderm, the suberin and its associated wax contained much smaller amounts of ferulate esters, in agreement with the in vitro ability of the FHT enzyme to conjugate ferulic acid with ω‐hydroxyacid and fatty alcohols. FHT down‐regulation did not affect the typical suberin lamellar ultrastructure but had significant effects on the anatomy, sealing properties and maturation of the periderm. The tuber skin became thicker and russeted, water loss was greatly increased, and maturation was prevented. FHT deficiency also induced accumulation of the hydroxycinnamic acid amides feruloyl and caffeoyl putrescine in the periderm. We discuss these results in relation to the role attributed to ferulates in suberin molecular architecture and periderm impermeability.     

矩镰荚苜蓿地下茎次生结构异常发育的解剖学研究

矩镰荚苜蓿是中国特有植物,分布于青藏高原东缘,具有发达的地下扩展茎。为探明矩镰荚苜蓿地下茎异常发育与高原气候适应的关系,该研究采用常规石蜡切片法对地下茎初生结构与次生结构进行解剖观察。结果表明：(1)与初生结构相比,矩镰荚苜蓿地下茎次生结构发育不均衡,仅有少量维管束正常发育,木质部发达。(2)地下茎次生生长会产生内、外两种周皮,外周皮由靠近韧皮部的内皮层细胞形成,内周皮由靠近木质部的髓细胞形成,内、外周皮形成后取代了表皮和初生结构中的主要薄壁组织,形成了较复杂的新防护系统。(3)外周皮向内隘缩或内周皮向外延伸都会引起地下茎的分裂,但暂未观察到两种分裂方式同时发生。研究认为,矩镰荚苜蓿地下茎形成内、外周皮与异常分裂,可以增强对干旱和寒冷胁迫的抵御能力,是矩镰荚苜蓿对青藏高原寒旱环境的适应策略。     

A novel form of epithelial wound healing of the embryonic epidermis

The embryonic epidermis of amniotes is a two-cell layer sheet with a periderm positioned superficial to the basal cell layer which, itself, attaches apically to the basal surface of the periderm and basally to the basal lamina. The presence of the periderm is essential to maintain the basal layer as a two-dimensional monolayer. Wounds to the epidermis that remove selectively just the periderm are healed by a stacking of the basal layer cells that constitute the wound bed. Basal cell stacking involves the desertion of the basal lamina by many of the cells so as to increase their contact area with other basal layer cells. This suggests that a preferential adhesion to the planar basal lamina is not important for the monolayered organization of the basal layer but, instead, association with inner surface of the planar periderm is the principal process that maintains the basal layer as a monolayer. The conversion of the basal layer from monolayer to multilayer during wound healing diminishes its planar area, resulting in movement of the wound borders toward the center of the wound. This is a novel scenario for wound healing.     

Phylogenetic analysis reveals that Rhabdopleura is an extant graptolite

A phylogenetic analysis of morphological data from modern pterobranch hemichordates (Cephalodiscus, Rhabdopleura) and representatives of each of the major graptolite orders reveals that Rhabdopleura nests among the benthic, encrusting graptolite taxa as it shares all of the synapomorphies that unite the graptolites. Therefore, rhabdopleurids can be regarded as extant members of the Subclass Graptolithina (Class Pterobranchia). Combined with the results of previous molecular phylogenetic studies of extant deuterostomes, these results also suggest that the Graptolithina is a sister taxon to the Subclass Cephalodiscida. The Graptolithina, as an important component of Early–Middle Palaeozoic biotas, provide data critical to our understanding of early deuterostome phylogeny. This result allows one to infer the zooid morphology, mechanics of colony growth and palaeobiology of fossil graptolites in direct relation to the living members of the clade. The Subdivision Graptoloida (nom. transl.), which are all planktic graptolites, is well supported in this analysis. In addition, we recognize the clade Eugraptolithina (nov.). This clade comprises the Graptoloida and all of the other common and well‐known graptolites of the distinctive Palaeozoic fauna. Most of the graptolites traditionally regarded as tuboids and dendroids appear to be paraphyletic groups within the Eugraptolithina; however, Epigraptus is probably not a member of this clade. The Eugraptolithina appear to be derived from an encrusting, Rhabdopleura‐like species, but the available information is insufficient to resolve the phylogeny of basal graptolites. The phylogenetic position of Mastigograptus and the status of the Dithecoidea and Mastigograptida also remain unresolved. □ Biodiversity, Cambrian, Hemichordata, Deuterostomia, Ordovician.     

东秦岭下志留统的笔石

笔石采自河南淅川下志留统张湾组,其时代与华中区龙马溪组相当。包含Ｄ．ｔｒｉａｎｇｕｌａｔｕｓ,Ｏ．ｃｏｍｍｕｎｉｓ和Ｍ．ｓｅｄｇｗｉｃｋｉｉ３个笔石带,可以与国内外同时代笔石带相对比。共记述正笔石目２科９属１５种,其中含２新种和１新亚种。     

Histochemical Probing of Potato Periderm with Neutral Red: A Sensitive Cytofluorochrome for the Hydrophobic Domain of Suberin

A technique is described which uses the lipid fluorochrome neutral red as a cytochemical probe to detect the hydrophobic domain of the lignosuberin matrix in native and wound periderm of potato tuber. Toluidine blue O is used as a counterstain to quench autofluorescence. The neutral red technique appears to be specific for the hydrophobic/lipid domain of suberin and is significantly more sensitive than Sudan III and IV. The fluorochrome was extensively used on paraffin-embedded tissue with excellent results but also worked on freehand sections of fresh periderm tissue. In tuber tissue undergoing wound-healing, the pattern of suberin fluorescence obtained with the neutral red probe was identical in specificity to the color pattern obtained with Sudan III/IV, but somewhat different than that observed when berberine was used. Results obtained with the neutral red probe and berberine probe visually demonstrated that during ligno-suberin biosynthesis, the depositions of hydrophobic/lipid and phenolic/lignin-like components in potato tuber periderm were separate processes. The deposition of these components does not necessarily require their simultaneous presence because the fluorescence from these probes showed that the components were not consistently present together on the cell walls.     

华南特马豆克期笔石地层分带及全球对比

特马豆克阶是奥陶系底部第一个阶,笔石是特马豆克阶高分辨率地层划分与对比的重要化石类群。江南斜坡带是我国早奥陶世特马豆克期漂浮笔石分异度和丰度最高的相区之一,位于该区的湖南益阳南坝剖面,发育有完整的上特马豆克阶笔石地层,特马豆克阶-弗洛阶界线附近地层连续,上特马豆克阶笔石地层研究已取得较大进展,但下特马豆克阶地层缺乏系统研究。近年来,通过对该剖面笔石标本的不间断采集,新识别出下特马豆克阶笔石带Rhabdinopora flabelliformis parabola带。到目前为止,湖南益阳南坝剖面特马豆克阶可以识别出5个笔石带,自下而上依次为:Rhabdinopora flabelliformis parabola带、Adelograptus tenellus带、Aorograptus victoriae带、Araneograptus murrayi带以及Hunnegraptus copiosus带。基于目前已识别出的笔石带,参考国内外同期笔石地层资料,本文详细讨论华南特马豆克期笔石带序列,并与国内外同期地层进行精确对比。     

Placement of the Wenlockian/Ludlovian boundary in western New York State

Despite many years of detailed examination focused on the Silurian strata of New York State, the position of the Wenlockian/Ludlovian boundary has, to date, not been satisfactorily cstablished. Reccnt discovery of early Ludlovian graptoloid graptolites, however, provides the first conclusive biostratigraphic evidence for placement of this chronostratigraphic boundary within the New York sections. The carly Ludlovian genera Saetograptus and Spinograptus were recovered from a thin, but laterally persistent bed of argillaceous dolostone located near the base of the Goat Island Formation. This occurrencc indicates that the Wenlockian/Ludlovian boundary is at or near the contact between the Goat Island Formation and the underlying Gasport Formation, considerably lower than had previously been suspected. □ Silurian, Wenlockian, Ludlovian, graptolites, stratigraphy. biostratigraphy.     

Graptolites from glacial erratics of the Laerheide area,northern Germany

Ordovician and Silurian glacial erratics of the Laerheide area (Lower Saxony, north-western Germany) bear well-preserved graptolites. The faunas provide important information on the origin and transport direction of the sediments preserved in a kame, representing the Drenthe stadial of the Saalian glaciation. The faunas even include species not commonly encountered in the successions of mainland Sweden, from where the erratics presumably originated. The most common graptolites are from Upper Ordovician (Sandbian to Katian) limestones and from Katian black shales. More common, however, are greenish limestones, sand- and siltstones, often combined in the term ‘Grünlich-Graues Graptolithengestein’, in which upper Wenlock to Ludlow (upper Silurian) graptolites are common.     

Proliferation of human embryonic and fetal epidermal cells in organ culture

The morphology of human embryonic and fetal skin growth in organ culture at the air-medium interface was examined, and the labeling indices of the epidermal cells in such cultures were determined. The two-layered epidermis of embryonic specimens increased to five or six cell layers after 21 days in culture, and the periderm in such cultures changed from a flat cell type to one with many blebs. The organelles in the epidermal cells remained unchanged. Fetal epidermis, however, differentiated when grown in this organ culture system from three layers (basal, intermediate, and periderm) to an adult-type epidermis with basal, spinous, granular, and cornified cell layers. Keratohyalin granules, lamellar granules, and bundles of keratin filaments, organelles associated with epidermal cell differentiation, were observed in the suprabasal cells of such cultures. The periderm in these fetal cultures formed blebs early but was sloughed with the stratum corneum in older cultures. The rate of differentiation of the fetal epidermis in organ culture was related to the initial age of the specimen cultured, with the older specimens differentiating at a faster rate than the younger specimens. Labeling indices (LIs) of embryonic and fetal epidermis and periderm were determined. The LI for embryonic basal cells was 8.5% and for periderm was 8%. The fetal LIs were 7% for basal cells, 1% for intermediate cells, and 3% for periderm. The ability to maintain viable pieces of skin in organ culture affords a model for studying normal and abnormal human epidermal differentiation from fetal biopsies and for investigating proliferative diseases.     

Outgrowth dependency of forelimb regeneration on nerves in adult African clawed frog,Xenopus laevis

Summary The relationship between the size and shape of regenerative outgrowth and the quantity of innervation was studied in adult Xenopus laevis. The forelimbs, of which the nerve supply was artificially altered, were amputated midway through the stylopodium and were kept for 1 year. The regenerative outgrowths that formed in normal limbs with an intact nerve supply were mainly spike-shaped and occasionally rod-shaped. However, when the nerve supply to the distal part of the forelimb was augmented by surgically diverting ipsilateral sciatic nerve bundles, the quantity of innervation was increased to about two and a half times that of the normal limb. These hyperinnervated outgrowths were somewhat larger than those of the normally innervated outgrowths and the majority of them were oar-shaped, a type hardly ever encountered in normal regeneration. In contrast, when partial denervation was performed concomitantly with limb amputation, by ablation of the N. radialis at the shoulder joint, the quantity of innervation decreased to about one half that of the normal limb. The outgrowths obtained were spike-shaped in all cases, with their size being about half that of the normally innervated outgrowths. Furthermore, when both the N. radialis and N. ulnaris were ablated in the same way, the amputated limbs were mostly non-regenerative, but some of them regenerated small conical outgrowths. Based on these results, a discussion is presented concerning the relationship between a regenerative outgrowth and the innervation of the forelimb in Xenopus.