ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 987 



was localized in the individual cells by staining with iodine solution. 

 The vesicles are very large, round or oval cells, and it is the meta- 

 plasm, and not the protoplasm or nucleus which is stained. They are 

 especially associated with the arteries of Molluscs, and the author 

 maintains the probability of their wide Invertebrate distribution. 



As to their theoretic import, Mr. Blundstone points out (1) that 

 if the lacunar system of molluscs is partly enteroccelous, the presence 

 on the lacunar walls of the vesicular glycogenous cells is interesting, 

 since glandular surfaces seem specially characteristic of ectoderm 

 and endoderm ; (2) that since the specific gravity and nutritive quality 

 of the blood could be maintained by the discharge of the glycogenous 

 vesicles, a great objection against water inception by molluscs is 

 removed ; (3) that here one of the characteristic functions of the 

 vertebrate liver is readily discharged by widely distributed individual 

 cells. 



Molluscoida. 

 a. Tunicata. 



Egg's of Ascidians.* — M. A. Sabatier finds that the ovary of 

 Ascidians is primitively composed of an agglomeration of mesodermal 

 nuclei united by a small quantity of clear intermediate substance ; it 

 has, therefore, the constitution and characters of an embryonic con- 

 nective tissue in which the " protoplasmic atmospheres " are not dis- 

 tinctly limited. In adults this structure is found in those portions of 

 the ovary in which there is a fresh formation of ova. The ova arise 

 from corpuscles of this embryonic connective tissue ; and these, in 

 which are developed one or two granulations which become nucleoli, 

 form the nuclei of the ova. Around the nucleus a transparent colour- 

 less layer of protoplasm becomes set, and the egg is completed. 

 Around the egg there is formed a very delicate primary membrane 

 vhich appeals to belong to the intermediate substance of the con- 

 nective tissue of the ovary ; it forms the amorphous capsular mem- 

 brane. Below this membrane, and on the surface of the yolk, there 

 appear follicular elements which become the follicular cells. They 

 are not of foreign origin, but are formed in the yolk itself and elimi- 

 nated by it ; they become individual cells by each acquiring nucleus, 

 granulations, and limiting membrane ; as they multiply they form 

 a continuous layer round the egg ; they may remain stationary or 

 grow considerably, when they project from the surface of the egg. 

 Below them, and at their expense, a second membrane is formed ; 

 this subcapsular membrane becomes more or less thick ; in some 

 cases the follicular cells remain flattened, become hardened, and so 

 form a thick structureless cnvelojie. The so-called testa-cells, or 

 granular cells, represent an eliminated element ; they are imperfectly 

 developed, and may be called cellubjid globules. 'J'he intravittlline 

 corpuscles are masses of clear finely granular proto2)lasm which are 

 formed by concentration within the yolk, and, by passing towards 

 the Kurfaco, are at firbt follicular and afterwards granular ceils. 



• Mcin. Acad. Sci. Montj)Llli<r, x. (1885) pj). 1:^0-80 (1 i)ls.). 



