COMPARATIVE ASPECTS OF SUPERFICIAL CONDUCTION SYSTEMS IN ECHINOIDS AND ASTEROIDS

The spine-convergence response of sea urchins and the papula(deimal branchia) retraction response of starfish persist afterremoval of the central nervous system, but are blocked by scratchingthrough the skin. They are mediated therefore by diffuse superficialconduction systems capable of limited spread—to a fewcentimeters. The spine response does not bend around the ends of a cut, andtherefore its conduction system is not a nerve net, though probablynervous. Every sensory site is connected to every effector site,within centimeters, but only by straight lines. This curiousand unprecedented arrangement is not yet understood or anatomicallybased. Some plausible connectivities cannot be ruled out geometricallyas being too extravagant. The response is not a chain reflexrequiring spine movement or stretch on its far side. Facilitationof successive responses is not evident. The papula retraction response of starfish spreads around theends of cuts. Its conducting system therefore acts like a truenerve net, the first such system to be demonstrated in echinoderms.It is capable of limited spread and, like the sea urchin spines,central reflexes are normally superimposed to mediate widespreadcoordination.     

ASPECTS OF THE PHYSIOLOGY OF THE SHEEP TICK

Recent work on the ecology of the sheep tick has posed many problems of a physiological nature that could best be investigated by laboratory or by combined laboratory and field studies. Three subjects of relevance to sheep tick ecology are briefly considered in the following paragraphs.     

COMPARATIVE ASPECTS OF THE ONTOGENY OF TASTE

Pigs are proposed as a useful laboratory model for the investigationof taste preferences and other controls of ingestive behaviorin the newborn. Suckling pigs can be easily trained to feedthemselves from an artificial feeding apparatus so that intakecan be measured directly. In this manner preferences for glucose,sucrose, fructose and lactose were found in pigs 3 wk of age.The preference threshold for glucose is considerably higherthan that reported for more mature pigs. Taste aversion wasdemonstrated in suckling pigs 2 wk of age. After the taste ofglucose had been paired with LiCl injection, poisoned pigs didnot show the strong glucose preference shown by control pigs.In addition to oropharyngeal controls of intake, gastrointestinalcontrols of intake in the newborn pig were investigated.Loadsof milk or 5% glucose, but not 0.9% NaCl, given by gavage depressedsubsequent intake in piglets 1 wk of age. Caloric or glucostaticmechanisms, but not volume alone, appear to be involved in satietyin the newborn pig. ^*Supported by USPHS Special Fellowship 5F03 AM55321-02 to K.A.H.Request for reprints should be sent to Dr. K. A. Houpt, Dept.of Physiology, N.Y.S. College of Veterinary Medicine, Ithaca,New York 14853, U.S.A.     

右心室条束的比较解剖学研究

本文用５种动物的３７０例心脏，对右心室条束作了比较解剖学观察。狗右心室条束的出现率为９７％，兔６４％，牛５２％，猪３８％，羊２５％。牛、猪、羊和兔的右心室条事多附着室间隔和室前壁之间，狗的条束多附着前乳头肌或室间隔和前壁之间。动物的右心室要束可分暗红色条束和乳白色条束，暗红色条束主要由心肌纤维构成，条不周边的结缔组织中含有不细胞；乳白色条束主要由结缔组织和位于中央的呸细胞构成，心肌纤维少或缺如。心     

中国新石器时代居民体质类型及其承继关系

运用数理统计方法把我国新石器时代居民分为华南、华北两大类群,其中华北类群又可分为三个小类群。在人类发展过程中,南、北两群间及华北各类群间都发生过血缘混杂的过程。运用数理统计方法也可把我国旧石器晚期人类——山顶洞人和柳江人在体质特征上与我国新石器时代各组居民明显地区别开来。山顶洞人和柳江人分别代表我国旧石器晚期南北两个不同的地方类型。我国新石器时代居民的所谓澳大利亚—尼格罗人种或南亚人种特点可以追溯到我国旧石器时代晚期人类——柳江人、山顶洞人,这些特点是我国新石器时代组人类固有的特点,只不过在不同的类群中表现有所差异而已。     

STEM ANATOMY AND ASPECTS OF DEVELOPMENT IN TOMATO

Aspects of anatomical development were correlated with internodal growth in tomato plants, variety ‘Yellow Plum,’ grown for more than 3 months. Internodal length was measured weekly in control plants and those harvested for anatomical study. Gross structure indicated progressive development with increasing age. Primary xylem and phloem first mature in distinct strands and the strands are joined laterally by procambium to form a continuous vascular cylinder. Primary phloem occurs on the outer periphery of the procambium between the early-formed vascular strands. Successive periclinal divisions in the procambium during internode elongation give rise to pronounced radial seriations of the cells. Procambial derivatives are included in the cylinder of thick-walled, lignified vascular cells that become prominent after elongation ceases. Secondary xylem is of greater radial width in the stem sectors which include protoxylem. During early secondary growth, vessels develop in the secondary xylem only in these sectors. Nucleate fibers and rays constitute the remainder of the secondary xylem. The rays exhibit an organization noted in other plants of reduced growth habit. Some of these interpretations do not agree with those described for tomato in earlier studies, and they are discussed in relation to pertinent aspects of development.     

THE EXCHANGE OF PHOSPHATIDYLCHOLINE AND OF PHOSPHATIDYLINOSITOL IN SHEEP BRAIN

—The exchange of phospholipids between liposomes and brain mitochondria has been studied in the presence of pH 5·1 supernatant fluids derived from rat, guinea pig, sheep and ox brains. The exchange phenomenon was similar to that observed in liver and heart, but phosphatidylinositol and not phosphatidylcholine was the most rapidly exchanging phospholipid. The phosphatidylcholine exchange activity was purified 186-fold from sheep brain and the protein fraction contained two major and several minor protein species. The phosphatidylcholine and phosphatidylinositol exchange activities have been shown to have very similar molecular weights and isoelectric points. However, their behaviour in response to changes in liposomal surface charge suggested that separate proteins might be involved in stimulating the exchange of the two phospholipid classes.     

COMPARATIVE ASPECTS OF PLANT MORPHOGENESIS: A CELLULAR,MOLECULAR, AND EVOLUTIONARY APPROACH

Recent research on development and evolution has focused attention upon arabinogalactan proteins, dominated by hydroxyprolines covalently bonded to oligosaccharides. Glycoproteins, ubiquitous in land plants, form distinctive patterns of distribution during development. Applied to cultures of hepatics, inhibitors of proline hydroxylation produce phenotypes mimicking more primitive species. Since glycoproteins are associated chiefly with wall and membrane metabolism, genes controlling glycoproteins may promote adaptive diversity via mutations. Evidence favoring this hypothesis was found by comparisons between major groups of land plants. In angiosperms, specialized cell walls are the rule, but phylogenetic trends involving them are not found. More important are trends in the reproductive structures, well known to taxonomists. With respect to these traits, genotype-phenotype interactions are indirect, involving different gene systems. Recently proposed theories that rely upon undefined morphogens are rejected. Development is epigenetic, based upon successive interactions between regulators produced at various developmental stages, each stage being integrated with those that precede and that follow. To produce an adaptive phenotype, each successive stage is controlled in such a way as to interact favorably with the internal environment present when it appears.