ZOOLOGY AND BOTANY, MICKOSOOPY, ETC. 211 



a gill on the right side of the body of Pelta, though difficult to 

 demonstrate, proves that that animal is related to the Pleurobranchiata ; 

 other characters of its organization justify us in establishing for it 

 a distinct family. 



Around the buccal depression there open a large number of mucous 

 glands, not, as in some allied forms, consisting merely of a simple vesicle, 

 but giving rise to mulberry-like masses of racemose character. Each of 

 these masses or aggregates is provided with an excretory duct of some 

 length, and they sometimes not only surround but enter to some 

 extent into adhesion with the nervous centres. The radular apparatus 

 within the buccal bulb does not agree in structure with that of the 

 true Pleurobranchs, and another point of disagreement with them is to 

 be found in the characters of the stomach, which call to mind the 

 arrangements which obtain in the BuUidee ; there are in it four large 

 horny plates, the walls are very muscular, and the whole seems to have 

 the function of a gizzard. 



The gill of Pelta is not well developed, and possesses only three 

 or four respiratory lamellae ; it is connected with the heart by means 

 of the branchial vein ; while the heart and its two aortge could be 

 made out, the remainder of the circulatory system baffled the investi- 

 gator. The same remark applies also to part of the reproductive 

 system, but it is of interest to note that the author was able to make 

 some observations on a subject which is just now attracting so much 

 attention — the development of the spermatozoa. He finds that the 

 male vesicles present the appearance of a cell with a nucleus, in which 

 one may distinguish several hyaline granulations ; at the periphery 

 of the male cells there are a certain number of granulations, similar 

 to those of the nucleus. This observation leads to the supposition 

 that here, as in Helix (Duval), there is an endogenous formation of 

 nuclei. Free from these mother-cells we see a large number of " poly- 

 blasts " more or less developed ; in one in an advanced stage, each bud 

 or " spermatoblast " is seen to be only connected with the primitive 

 cell by a delicate peduncle which, later on, forms the anterior part of 

 the spermatozoon. The spermatoblasts continue to elongate, until at 

 last we have a large number of spermatozoa which are attached by 

 their heads. 



The oesophageal nerve-collar is formed by three pairs of ganglia 

 which are connected with one another by short commissures ; of these 

 the cerebroid ganglia are of a pale orange colour, while the pedal and 

 the visceral are more deeply orange. Tentacles being absent, it is 

 possible that olfactory organs are present, but the author was not able 

 to convince himself of this ; the eye has the ordinary Opisthobranch 

 structure, while the otocysts are of some size, one only being present 

 in each auditory cell. 



The author's investigations lead him to concur in the suggestion 

 of J. E. Gray, that the family Peltidce should be instituted for the 

 reception of this form. 



Tylodina is next dealt with, and its relations to Umbrella are par- 

 ticularly insisted on; differences in the number and form of the 

 teeth of the radula were observed to obtain with age ; the stomach is 



