ZOOLOGY AND BOTANY. MICROSCOPY, ETC. 247 



Regeneration in Littoral Gastropods.* — Paul' Pelseneer finds 

 that the tentacles of such Prosobranchs as Purpura and Nas&a are 

 regenerated more rapidly and regularly than those of terrestrial Pul- 

 monates. The regeneration of the eye takes place most rapidly in 

 young forms. The rate is hardly, if at all, lessened in darkness. The 

 tentacles are very slow to regain their original length, or the eyes their 

 diameter. 



Pelseneer also studied the regeneration of parts in the littoral Tur- 

 bellarian, Leptoplana, which is often found with traces of wounds. The 

 rate of the regeneration varies directly with the degree to which the 

 central nervous system is left intact. Where the part cut off is small, 

 there is often a rapid healing up along the cut margin, instead of a 

 regular regeneration, which is a slower process. 



8. Laniellibranchiata. 



Alimentary System and Heart of Arca.j — Martin Matthias has 

 made a detailed study of the alimentary system and heart in various 

 species of Area. The mouth lies behind the anterior adductor ; the 

 oesophagus is short and has a small, ventral diverticulum in A. angulata. 

 The stomach is relatively small, and does not keep pace with the growth 

 of the animal ; it consists of a dorsal portion, the stomach proper, and 

 a ventral portion, the stomach-intestine. In the stomach proper three 

 parts can be distinguished — the cardiac portion, the fundus, and the 

 pyloric portion, differing in relative sizes in different species. Both at 

 the anterior and posterior end of the stomach there is a small caecum. 

 The openings of the hepato pancreas differ in number (ten or more) and 

 in position. 



The epithelium of the stomach differs in different species. Most 

 striking is a band of high prismatic ciliated epithelium in the fundus of 

 A. barbata, into which phagocytes may penetrate, probably for the ab- 

 sorption of food. Over the whole intestinal epithelium there are uni- 

 cellular glands, which are probably digestive, and perhaps compensate for 

 the absence of salivary glands. 



All Arcacea have a " stomach-intestine " consisting of an intestinal 

 groove and a sheath around the crystalline style. The two regions are 

 partially separated by a prominent epithelial ridge with many unicellular 

 glands, some of which secrete the cystalline style. The chyme from the 

 stomach glides along the groove to the intestine proper. The epithelium 

 of the sheath of the crystalline style consists of high prismatic cells with 

 somewhat setose surfaces, which work the style into the stomach. 



In some Larnellibranchs the crystalline style is secreted in an 

 intestinal groove ; in others there is a special separate caecum for the 

 style ; in a third set there is a " stomach-intestine " succeeding the 

 stomach and divided into an intestinal groove and a style-sheath. 



The relation of the rectum to the heart differs in different species. 

 In A. platei and A. lactea the pericardium and ventricle are perforated 

 by the rectum. In A. barbata there is a complete separation of the 



* C.R. IXe Congress Internat. Zool. Monaco, 1914, pp. 172-3. 



t Jen. Zeitschr. Naturw., lii. (1914) pp. 363-444 (4 pis. and 5 figs.). 



