36 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Mollusca. 



Digestion in Cephalopoda.* — E. Bourquelot continues his 

 researches on this subject,| referring particularly to (1) the digestion 

 of amylaceous matters and (2) of saccharose, (3) the function of 

 the salivary glands, (4) the liver, and (5) the meclianism of digestion. 



The food reaches the stomach direct ; the crop of the Octopus seems 

 to he only a kind of surjilus reservoir ; there it is subjected to the action 

 of the digestive fluids which come from the liver and the pancreas 

 passing by the caecum. The proteid matters and the hydrocarbons 

 are digested, the fats emulsionized, and the chyle goes directly into 

 the intestine without passing by the ceecum. At the conclusion of 

 digestion there is found in the cfecum and often even in the hepatic 

 canals a small brown column which might be taken for digested food. 

 It is, however, only a mass of hepatic cells detached from the gland. 

 A similar column has already been noticed by Plateau at certain 

 periods of digestion in the excretory canals of the abdominal gland of 

 the Spiders. 



Development of Bithynia tentaculata.| — P. B. Sarasin, in his 

 introduction, points out that although the embryos of this fresh-water 

 Pulmonate Gasteropod are small and oi^aque, it is possible to make a 

 good series of sections, in consequence of the comparatively small 

 amount of yolk-material which is found in the endodermal cells. 

 These are always sharply marked off, and have a distinctly cylindrical 

 form. 



The rounded yellowish ovum presents an elevation which appears 

 to be, but is not, the point at which the directive corpuscle is extruded ; 

 indeed it is only as it disappears that the corpuscle is to be seen 

 at the opposite pole of the egg. A period of rapid cleavage appears 

 to be followed by one of repose ; four larger polar cells are soon to 

 be distinguished from a number of smaller ones ; the gastrula, after 

 formation, closes up again, and forms a complete and solid sphere — 

 the pseudogerm-spliere. At its thickened part there arise two solid 

 processes, one of which is distinguished by a slight depression on it, 

 which soon becomes converted into the mouth. At this stage there 

 is no indication of any velum ; when the latter does come into existence 

 it has at first the appearance of two rows of ciliated ectodermal cells. 

 The process connected therewith forms the foot, while the other, by 

 an ingrowth of cells, is the seat of the future shell-gland. The author, 

 in opposition to the views of various embryologists, expresses his 

 belief that in all Gasteropoda the original gastrula-mouth (blastopore) 

 becomes closed up. 



In the second section the velum, and jirimitive kidney {ansae) are 

 dealt with ; the name of ansae is applied to the chords of transparent 

 vesicular ciliated cells, which are found inserted at the sides of the 

 mouth, and which, in the embryo, have the function both of velum and 

 of primitive kidneys ; the author devotes some attention to demon- 



* Comptcs Rendus, xcv. (1882) pp. 1174-6. 



t Cf. this Journal, ii. (1882) p. 30. 



i Arbeit. Zool.-Zoot. Inst. Wiirzbuig, vi. (1882) pp. 1-68 (7 pis.). 



