TRANSPORT OF UNCONTAMINATED AND MOLLUSCICIDE-CONTAINING FOOD IN THE DIGESTIVE TRACT OF THE SLUG DEROCERAS RETICULATUM (MULLER)

By X-ray analysis of food transport in the alimentary tractof Deroceras reticulatum it was shown that even ten hours afteringestion of a thorium sulfate-containing bait, this materialcan be detected in the crop. After 2.5 h, some parts of labelledfood passes down from the anterior to the posterior part ofthe gut. After 13 h, thorium sulfate-containing material canbe observed only in the gut. After 19 h, no more labelled materialis present in the alimentary tract of the animals. After addition of Cloethocarb, the animals feed on only smallamounts of food. The labelled material only enters the anteriorpart of the gut. After ten hours, the food does not move anymore and does not leave the crop even 19 h after feeding. After molluscicide application, the crop epithelium is moreinfolded than in control animals and the cells are elongated.After 30 h, cells protrude into the lumen of the digestive tract. (Received 11 May 1992; accepted 26 June 1992)     

中华稻蝗消化道内分泌细胞的鉴别与定位

采用整块组织Grimelius银染法和过氧化物酶标记的链霉亲和素免疫组织化学技术,结合生物统计学分析,对中华稻蝗Oxya chinensis消化道内分泌细胞进行鉴别与定位。结果表明：嗜银细胞分布于中华稻蝗的胃盲囊、中肠和后肠各段,以中肠和直肠中最多（P<0.05）, 前肠中未见分布。免疫组织化学法检测出了五羟色胺（5-hydroxytryptamine, 5-HT）、 胃泌素（gastrin, Gas）、 胰高血糖素（glucagon, Glu）和胰多肽（pancreatic polypeptide, PP）细胞, 未检出生长抑素（somatostatin, SS）细胞。免疫阳性细胞分布于中肠和后肠中, 前肠中未见分布。5-HT细胞和Gas细胞均主要分布于胃盲囊、中肠及直肠中,且均以直肠中最多（P<0.05）。Glu细胞在胃盲囊及整个中、后肠均有分布, 在中肠和直肠中最多（P<0.05）。PP细胞主要分布于中肠、回肠和直肠中,中肠中分布密度最大（P<0.05）。本研究显示中华稻蝗消化道中存在多种内分泌细胞,它们的分布情况与其他节肢动物相比存在一定的共性,也有其一定的特异性,可能与中华稻蝗特定的消化道结构和消化生理功能有关。     

A PLANIMETRIC STUDY OF MORPHOLOGICAL VARIABILITY IN THE DIGESTIVE DIVERTICULA OF LITTORINA LITTOREA (LINNAEUS) AND MYTILUS EDULIS LINNAEUS

The inter-and intratubular morphological variability in thedigestive diverticula of Littorina littorea and Mytilus edulishas been investigated by planimetric procedures. Five parametershave been measured: mean epithelial thickness (MET), mean diverticularradius [MDR], mean luminal radius (MLR), MLR/MET ratio and MET/MDRratio. The results indicate that irrespective of the patternof tubule organization within the digestive diverticula (whethertubule types are clustered or not), variability between individualsis greater than that between zones of the digestive gland. Thishas implications for the design of sampling strategies in investigationsof the morphology of digestive diverticula in physiologicaland pathological studies. The variability in the epithelialthickness within diverticular sections is of minor relevancein assessing the overall condition of the digestive gland inthese studies, because variability in epithelial thickness betweentubules is significantly greater than within tubules in bothspecies. (Received 10 March 1989; accepted 16 October 1989)     

中华刺鳅消化系统形态与组织学研究

应用活体解剖和光镜技术对中华刺鳅消化系统形态与组织学特征进行了研究。结果显示:中华刺鳅属典型的无鳔管、有胃鱼类,消化道较短,约为体长的45%,整体呈“Z”字形。食道很短,后与胃相联,胃呈“V”型,胃分为贲门部、胃底部和幽门部,贲门胃自食道末端到胃的底部都具有丰富的腺组织分布,其长度也是胃部最长的,约占中华刺鳅消化管长度的23%。胃底部的肌肉发达较厚,但仅贲门部有丰富的腺组织。消化道各段在组织结构上差异显著。胃前,消化道肌肉层内环肌与外纵肌厚度之比自前向后逐渐增大,杯状细胞数量自前向后逐渐减少;胃后,肠道肌肉层内环肌与外纵肌厚度之比则逐渐减小,杯状细胞数量逐渐增多。消化腺分为肝脏和胰腺,肝脏与胰脏为独立的两个器官,胰脏分散分布于胃与肠道周围的系膜内,肉眼可见。未发现类似鲤科鱼类弥撒于肝脏或脾脏内的胰腺结构。中华刺鳅以日本沼虾和秀丽白虾为主要摄食对象,性凶猛,为典型的肉食性鱼类。     

银鲳消化道形态与组织学结构特征及其消化酶活性

为了解银鲳(Pampus argenteus)消化道结构特点与其功能及食性的相关性, 采用解剖、石蜡切片、AB-PAS染色及酶活性检测技术对银鲳消化道的形态、组织结构、黏液细胞分布及消化酶活性进行研究。结果显示, 银鲳的消化道由口咽腔(舌)、食道侧囊、食道、胃及肠构成, 胃肠交界处有很多幽门盲囊。食道侧囊呈椭球形, 食道粗短, 胃呈U型, 肠有多个盘曲, 肠指数为2.03。舌上皮内有少量味蕾及较多黏液细胞。食道侧囊、食道、胃及肠均由黏膜层、黏膜下层、肌层及浆膜组成。食道侧囊内皱襞较发达, 被覆复层扁平上皮, 内含较多黏液细胞, 且以Ⅳ型为主, 皱襞顶端及侧面有内含角质刺的次级突起; 黏膜下层及肌层中有固定皱襞的骨质脚根; 侧囊内胃蛋白酶活性较高。食道内皱襞较高, 被覆复层扁平上皮, 内含较多黏液细胞, 且以Ⅳ型为主。胃内皱襞发达, 被覆单层柱状上皮, 未见黏液细胞分布; 胃腺发达, 胃内蛋白酶活性较高。肠道内褶襞多, 高度呈先下降后上升趋势, 黏液细胞密度前、中肠较高, 后肠较低, 且均以Ⅰ型为主; 肠道内胰蛋白酶、脂肪酶、淀粉酶及碱性磷酸酶活性较高。幽门盲囊组织结构与肠相似。银鲳的消化道结构特点、黏液细胞分布及消化酶活性与其功能及偏肉食的杂食性相适应。     

Histological structure of the digestive tract,liver, and pancreas of Ambassis nalua (Hamilton, 1822) with ultrastructural details of the gastric gland

The scalloped perchlet Ambassis nalua is one of the dominant fishes in the Estuarine Pranburi River, Thailand. It is suggested that this fish is in the secondary trophic level with a carnivorous nature. Studies on digestive system will help us further identify the niche of this species in the food web/food chain. The present study therefore aimed to report the detailed structure and ultrastructure of A. nalua digestive system. Fish samples (n = 30) with a total length of 5.7 ± 0.5 cm were obtained using beach seines from the Estuarine Pranburi River. Their digestive tract length and intestine coeficient were 3.6 ± 0.07 cm and 0.91, respectively. Light microscopic observation showed that the digestive wall comprised four layers, namely mucosa, submucosa, muscularis, and serosa. The prominent mucous-secreting cells were found in the mucosal oesophagus. The stomach had many gastric folds, with height and width being 649.76 ± 85.15 and 370.30 ± 68.56 μm, respectively. Gastric glands were found in the anterior stomach but not in the posterior stomach. Each gastric gland was made up of a single type of columnar cells. The gastric cells were ultrastructurally characterized by numerous mitochondria and well-developed secretory granules of varying sizes. A few small vacuoles were also identified in the apical area of the gastric cells. The intestine had two regions (anterior and posterior intestines), and pyloric caecum was absent. The density of the goblet cell was significantly higher in the posterior intestine. These results provide basic knowledge of the digestive system of A. nalua, and the low intestine coefficient and the absence of pyloric caecum suggest the carnivorous feeding habit of this species.     

8种有胃真骨鱼消化道降钙素免疫活性细胞的定位及形态学研究

应用过氧化物酶标记的链霉卵白素免疫细胞化学技术对鳜、大口黑鲈、尼罗非鲫、短盖巨脂鲤、鲇、黄颡鱼、黄鳝和乌鳢等8种有胃真骨鱼消化道粘膜中降钙素免疫活性内分泌细胞进行了免疫细胞化学定位及形态学比较．结果表明,在尼罗非鲫、鳜和大口黑鲈消化道的任何部位均未见到阳性反应。另外5种鱼消化道的不同部位可不同程度地见到阳性细胞,其中黄颡鱼的整个消化道均有降钙素免疫活性的阳性反应;黄鳝和乌鳢的肠道中则无阳性反应,但在它们的胃以及黄鳝的食道中见到阳性细胞;鲇除食道中没有发现阳性细胞外,消化道各段中均有阳性细胞的存在;短盖巨脂鲤则仅在食道中发现阳性细胞。降钙素免疫活性细胞在肠道中的形态大多为长校形,胞体膨大,胞核是空油状,有两个相对的胞突分别伸向肠腔和基膜;胃中的降钙素细胞在位于胃上皮细胞之间时形状多为较短的梭形,而位于胃腺中时其形状较前者更加粗、短,胞突短小,常常呈不规则形状沿胃腺管边缘分布。     

THE FUNCTIONAL ANATOMY OF THE GUT OF THE PROSOBRANCH GASTROPOD POMACEA CANALICULATA AND OF SOME OTHER PILIDS

The structure and functioning of the gut of Pomacea canaliculata (D'Orb.) has been investigated using living and preserved material. Anatomical studies were also carried out on preserved specimens of Pila globosa, Turbinicola saxea and Lanistes ovum bangweolicus .
The gut of pilids is specialised for a macrophagous diet, usually of aquatic angiosperms. The mid-oesophagus is a crop for storage, and the stomach has a large triturating gizzard developed from the gastric shield area. This is the site of extra-cellular digestion; there is no intra-cellular digestion in any part of the gut. The ducts of the digestive gland open into a special region of the stomach, the vestibule, which is histologically similar to them. The style sac begins the compacting of the faeces, which is completed in tho intestine. There is no evidence that absorption ocrurs in the epithelium of tho stomach or intestine; soluble products of digestion are carried into the digestive gland, which is the main site of absorption. Its activity is supplemented by amoebocytes entering the lumen of the style sac and intestine. Two types of cell occur in the gland, one type producing digestive enzymes and absorbing soluble products of digestion, the other type being excretory in function. There is no sign of phagocytosis in either. The excretory activity of the kidney is further supplemented by an anal gland.     

BIOCHEMICAL DETECTION AND IMMUNOHISTOCHEMICAL LOCALIZATION OF ENKEPHALIN-LIKE SUBSTANCES IN PERIPHERAL TISSUES OF THE SCALLOP PECTEN MAXIMUS (LINNAEUS)

This study focused on the biochemical detection of the methionine-enkephalin-,leucine-enkephalin-and methionine-enkephalin-arg-gly-leu-likepeptides in the stomach, digestive gland, male and female gonads,muscle, gill and mantle of the scallop Pecten maximus usingspecific radioimmunoassays. Enkephalin-like substances weremainly present in the stomach and in the digestive gland, whereleucine-enkephalin-and methionine-enkephalin-arg-gly-leu-likepeptides were the predominant of these substances. In the gonads,muscle, gill and mantle, the enkephalin-like contents were closeto the sensitivity threshold of the enkephalin antibodies. Theenkephalin-like contents measured in September, in the digestivecomplex, were significantly higher than in December, when thebivalves have undergone a period of starvation. Immunohistochemicalassays were performed on the stomach and the digestive glandto localize the enkephalin-like materials. In these organs,which are the main sites of the digestive process in Bivalyia,the enkephalin-like materials were mainly confined to the endocrine-likecells. These results suggest that in Pecten maximus, opioidsmay be involved in the digestive processes mainly through enkephalin-endocrine-likecells. (Received 29 December 1994; accepted 1 May 1995)     

龟足消化系统形态和组织学特点

应用光学显微镜观察龟足（Capitulum mitella）消化系统的形态和组织结构。龟足的消化系统包括消化腺和消化道。消化腺一对,呈长囊状,含有分泌细胞（B细胞）、吸收细胞（R细胞）、储存细胞（F细胞）和胚细胞（E细胞）4种类型细胞。消化道呈U型,由口、食道、胃、肠、直肠和肛门组成,各部分的结构由内到外可分为黏膜层、黏膜下层、肌层和外膜4层。口器为咀嚼型,包括一片上唇、一对触须、一对大颚以及两对小颚。食道细短,具几丁质层但无基膜,管壁向腔内突起形成明显的纵褶突;食道前段的环肌特别发达,同时独有放射肌。胃略呈球袋状,肠较长;胃和肠的组织结构相似,没有几丁质层,上皮细胞都有发达的微绒毛。直肠细长,外膜分布有16组纵肌;直肠前段的组织结构与胃、肠相似,而直肠后段有几丁质层覆盖,黏膜层、黏膜下层、肌层和外膜渐退化,16组纵肌渐发达。肛门16组更加发达的纵肌挤入上皮细胞下方,在外膜外另出现一层明显的环肌。龟足消化道各部分的组织结构差异明显,反映了它们功能的差异。     

On the Fine Structure of the Alimentary Tract of Cephalodiscus gracilis (Pterobranchia,Hemichordata)

The U-shaped alimentary tract of Cephalodiscus is of exclusively epithelial structure; on the basis of fine structural criteria the entire tract can be divided into two large subdivisions: an anterior one with mouth, mouth cavity, pharynx and oesophagus, and a posterior one with stomach and intestine. The anterior subdivision is built up of a relatively uniform, innervated, pseudostratified, ciliated epithelium with mucus cells which are concentrated in the initial parts of the mouth cavity. Cilia and mucus presumably constitute a mechanism transporting food particles into the stomach. In the area of the gill slits specific vacuolated cells occur which may lend rigidity to the walls of the slits. The gastric epithelium consists of prismatic cells characterized by, among others, large inclusion bodies, which may represent digestive vacuoles, small dense rod-shaped granules and an elaborate system of microridges, at the base of which abundant endocytotic vesicles occur. The dorsal gastric pouch contains cells rich in rough ER and secretory granules, probably containing digestive enzymes. Thus morphological evidence points both to intra- and extracellular digestion. The intestinal epithelium resembles that of the stomach, however, it is lower, its organelles are fewer and it bears, beside cilia, mainly microridges, which towards its distal end become sparse. Both in the gastric and intestinal epithelium small granulated cells have been found, which presumably represent endocrine cells.     

Microanatomy of the digestive tract and accessory organs of the Japanese flathead (Inegocia japonica Cuvier, 1829) (Scorpaeniformes,Platycephalidae)

The Japanese flathead, Inegocia japonica Cuvier, 1829 is a commercially important fish in small-scale coastal fisheries in Thailand; however, an explanation of its digestive biology is missing. This study describes the digestive tract and accessory organs of I. japonica, using morphological and histological methods. The fish (10 individual fish, 24.5 ± 0.98 cm in total length) were obtained from Libong Island, Thailand. Integrated morphological and histological data showed that the digestive tract was composed of oesophagus, stomach, pyloric caeca and intestine, with accessory organs. All digestive tracts consisted of four layers, including mucosa, submucosa, muscularis and serosa. Two stomach regions were identified (cardiac and pyloric stomachs). Several clusters of gastric glands were identified in the cardiac stomach. Each gland was a unicellular structure. The apical surface of this gland contained the vacuolar cell. The intestine was lined with a simple columnar structure with goblet cells that was similar to pyloric caecum. Goblet cells were rare in the anterior intestine, in contrast to the posterior intestine where goblet cells were abundant. The numerous of hepatocyte was mostly observed in the liver, whereas an exocrine acinar cell of pancreas was also identified. The results of our observations provided the first information of the digestive tract of I. japonica and can be applied to advanced study, such as physiology and histopathology.     

Morphological and histochemical features of the digestive tract of Leiarius marmoratus (Gill, 1870)

Leiarius marmoratus, a freshwater catfish from Pimelodidae family, shows great biological and commercial relevance because of its geographic distribution and adaptation to fish-farm. The knowledge of the morphological characteristics of the digestive tract is fundamental to the understanding of fish physiology and nutrition, which helps in the planning of diets to provide better management and success in fish farming. Thus, this work described the morphology and histochemistry of the digestive tract of L. marmoratus adults. After euthanasia, the animals were dissected for analysis of the digestive tract. The oesophagus is a short and distensive organ with longitudinal folds that allow the passage of large food, e.g., other fishes. Oesophageal mucosa layer shows a stratified epithelium with goblet cells and club cells. The secretion of goblet cells is composed of neutral and acidic mucins that are anchored in the epithelium luminal face by epithelial cells fingerprint-like microridges, lubricating the surface to facilitate the food sliding. Club cells have protein secretion that can be involved in alarm signals when epithelium is damaged and in immunological defence. The saccular stomach is highly distensible to store large food. Gastric mucosa layer is composed of epithelial cells with intense secretion of neutral mucin to protect against self-digestion of gastric juice. Cardiac and fundic regions of stomach show well-developed gastric glands composed of oxynticopeptic cells. These cells have numerous mitochondria, highlighting their intense activity in the synthesis of acid and enzymes. The intestine is divided into three regions: anterior, middle and posterior. Although it is a short tube, intestine shows longitudinal folds and microvilli of enterocytes to increase the contact surface. These folds are higher in the anterior region of the intestine, highlighting their function in digestion and absorption. Intestinal goblet cells have acidic and neutral mucins that lubricate the epithelium and aid in digestive processes. These cells increase in number towards aboral, and they are related to the protection and lubrication to expulsion of faecal bolus.     

Cytochemical features of the digestive tract mucosa of Hemisorubim platyrhynchos (Siluriformes: Pimelodidae)

Membranous organelles, acid glycoconjugates and lipids were characterized in the digestive tract mucosa of Hemisorubim platyrhynchos by cytochemistry techniques. Two types of mucous‐secreting cells were observed in the digestive tract epithelium: goblet cells in the oesophagus and intestine and epithelial cells in the stomach. These cells had a Golgi apparatus more developed than the other cell types. The cytochemical analysis revealed that secretory granules are reactive to acid glycoconjugates, varying in reaction intensity according to the region of the digestive tract. Acid glycoconjugate reactions were also observed in oesophageal epithelial cell microridges and in enterocyte microvilli. In the digestive tract, acid glycoconjugates act to protect the epithelial surface, increasing mucous viscosity, which facilitates the passage of food, prevents the binding of parasites and facilitates their removal. Through lipid staining, a coated membrane was observed around each secretory granule of the oesophageal and intestinal goblet cells, while gastric epithelial cells granules were fully reactive. Oxynticopeptic cells of the gastric glands showed lipid droplets in the cytoplasm and also in the mitochondrial matrix, which act as an energy reserve for these cells that have a high energy demand. Enterocytes showed a well‐developed smooth endoplasmic reticulum, especially in the apical region of the cell, being related to absorption and resynthesis of lipids.     

Microscopic anatomy and ultrastructure of the stomach of Porcellio scaber (Crustacea,Isopoda)

Summary From the micromorphological viewpoint, the stomach is by far the most complicated part of the digestive tract of Porcellio scaber. All parts are shown in electron micrographs. The simplest inner surface of the stomach is the dorsal part, which has an unpaired flap directed posteriorly (lamella dorsalis). The lateral walls carry the lateralia, superolateralia and lamellae annulares. The most complicated region of the stomach is the ventral surface with its anterior primary filter, the adjacent masticatory areas, the posterior secondary filter on the lateral sides of the inferomedianum and the inferolateralia. Ingested food can be filtered twice: first on the primary filter and then on the secondary filter. The digestive fluid secreted in the midgut glands can be conveyed on the same route as the filtrate of the gastric juice, but in the other direction. The posterior part of the stomach is wrapped by a ring-shaped fold of the anterior hindgut, thus making seven epithelia closely apposed to each other.     

The tidal rhythm of feeding and digestion in the pacific oyster, Crassostrea gigas (Thunberg)

A study has been made of the processes of extra- and intracellular digestion in the Pacific oyster, Crassostrea gigas (Thunberg) over two 24-h cycles in winter and summer.The results show that the digestive processes are discontinuous and related to the tidal cycle. Variations in tidal height resulting from a diurnal inequality of the tide affect both the relative dissolution of the crystalline style and the relative lengths of the constituent phases of the intracellular digestive process in the digestive diverticula. On a seasonal basis the style is present for a greater length of time in winter and, conversely, remains dissolved longer in summer. A seasonal variation in the structure of the digestive tubules has also been found.The results confirm conclusions reached earlier that the processes of extracellular digestion in the stomach and intracellular digestion in the digestive diverticula of intertidal bivalves are both discontinuous, alternate, and irrevocably interrelated since breakdown of the digestive cells of the digestive diverticula following intracellular digestion results in the dissolution of the crystalline style. The arrival of food in the stomach has a minimal effect upon the style. Moreover, the cytological structure of the digestive diverticula of C. gigas undergoes a series of synchronized changes related to the tidal cycle.     

MONOPHASIC AND DIPHASIC DIGESTIVE CYCLES IN VENERUPIS DECUSSATA AND CHLAMYS VARIA

Feeding and digestive cycles in Chlamys varia and Venerupisdecussata are identified and shown to relate to a tidal cycle.The processes of digestion within the diverticula of the twospecies are very different. The tubules of Venerupis are synchronizedand exhibit a monophasic cycle completed within a twelve-hourperiod, facilitating feeding at the next cycle of the tide.The digestive process of Chlamys requires twenty-four hoursand to accommodate feeding at each twelve-hour tidal cycle thetubules within the diverticula exhibit two different digestivephases simultaneously so that a diaphasic cycle is apparent.The pH of the mantle cavity and regions of the digestive tractand the formation and dissolution of the crystalline style areshown to be related to the tidal cycle. ^*Department of Brewing and Biological Sciences, Heriot-WattUniversity, Chambers Street, Edinburgh, EH1 1HX. (Received 22 March 1978;     

ANATOMY AND RELATIONSHIPS OF THE BONE-FEEDING LIMPETS, COCCULINELLA MINUTISSIMA (SMITH) AND OSTEOPELTA MIRABILIS MARSHALL (ARCHAEOGASTROPODA)

The anatomy of Cocculinella minutissima (Smith, 1904) and Osteopeltamirabilis Marshall, 1987 is described. Both species belong tothe Lepetelloidea and are closely related to Addisonia Dall,1882, the anatomy of which has been recently described by theauthor. Commonly derived (symapomorphic) characters of all threegenera are found especially in the genital system (hermaphrodites,tcstis and ovary separated, with separated ducts, open seminalgroove to the unmodified right cephalic tentacle), and in thealimentary tract (paired oesophageal glands). Distinct similaritiesin genital and excretory system (large right kidney isolated;hermaphrodites, separated gonads) with the Pseudococculinidae,Pyropeltidae and Lepetellidae justify a uniting superfamilyLepetelloidea, the anatomy of which is quite different fromthat of the Cocculinoidea (Cocculinidae and Bathy-sciadiidae) Osteopelta has retained certain primitive characters (rhipidoglossateradula, true stomach), but is specialized in having a snout-likehead, a concentrated cerebropedal ring, and secondary gill leaflets(vestigial gill in Cocculinella, distinct gill leaflets in Addisonia).Cocculinella and Addisonia share additional synapomorphic featuresof the posterior alimentary tract (reduction of stomach, intestineforms a large sac, midgut gland contains dark granules). Severalaut-apomorphies of each genus justify their status as distinctfamilies. Relationships to the (coiled) Choristellidae, whichfeed on empty egg-cases of sharks or skates (as do addisoniids)and have a cocculinellid-like radula type, are discussed ^*Present address: Insitut fr Zoologie der Universitat, Technikerstr.25; A-6020 Innsubruck, Auttria (Received 10 March 1987;     

ULTRASTRUCTURAL AND ECOLOGICAL ASPECTS OF THE DEVELOPMENT OF CHLOROPLAST RETENTION IN THE SACOGLOSSAN GASTROPOD ELYSIA TIMIDA

Elysia timida is a common and endemic inhabitant of shallowand very well lit waters in the Mediterranean. This sacoglossanslug retains functional symbiotic chloroplasts derived fromits algal food, Acetabularia acetabulum, although the chloroplastsare not transmitted in the spawn. After hatching and until day12, Elysia timida juveniles do not retain these chloroplastsin the digestive gland. However, newly hatched juveniles retainchloroplasts from Cladophora dalmatica. Development varies seasonallybetween direct (December to April) and lecithotrophic (October,November and May), and this variation may be an adaptation toseasonal calcification of the algal food Acetabularia acetabulum. (Received 12 February 1991; accepted 15 July 1992)     

EVOLUTION, DURING DIGESTION, OF THE BACTERIAL FLORA IN THE ALIMENTARY SYSTEM OF HELIX ASPERSA (GASTROPODA: PULMONATA): A SCANNING ELECTRON MICROSCOPE STUDY

The use of scanning electron microscopy (SEM) allowed a studyof the distribution of bacteria in the various digestive organsof the snail Helix aspersa Müller. The bacteria are enclosedby mucous secretions (mucous film or mucous grains) and sometimesattached on the cilia of some of the digestive walls. Accordingto the food that was given to the snails, different morphologicaltypes appeared, two of which dominated. Adult snails were fasted for 4 days, given a dehydrated artificialfood and then sacrificed at different times during digestion.The presence of bacteria may be related to the time of digestion.In fact, bacteria seem to accompany the food mass; they developmostly in the stomach and in the intestine where they may helpdigest the food. Fasting or hibernating snails do not possess bacteria in thealimentary lumen or on the digestive walls. However, the residualfaeces localized in the distal, intestinal lumen, lodge greatquantities of bacteria. From these results, the endogenous or/and exogenous existenceof the bacterial flora in alimentary system of Helix aspersais discussed. (Received 26 June 1989; accepted 16 October 1989)