ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 627 



formed by the agglutination of granules of various sizes, but large 

 granules are formed by the fusion of several smaller ones. 



The formation of the byssus is regarded by the author as being 

 very simple ; the walls and the laraellce of the byssus-cavity con- 

 tinually secrete a byssogenous matter ; the lamellae in the anterior 

 and narrow part of the cavity unite and fuse with one another, while 

 the narrower shape of the orifice gives the byssus-threads their form. 

 Owing to the relations of the ventral groove of the foot each byssus- 

 thread is immediately fused to the main trunk. 



The author doubts the correctness of A. Miiller's view that there 

 is an agglutinating and a byssogenous substance; and speaks severely 

 of the artificial character of that author's classification of the species. 



General Characters of Cymbulia.* — The Pteropoda being so 

 purely pelagic in their habit, places them out of the reach of zoologists 

 in general ; and even systematic writers, as in other cases, are often 

 misguided by incorrect figures and descriptions made up probably 

 from scanty or defective data, but which have, nevertheless, been 

 handed down to us with a show of truth. Dr. J. D. Macdonald was 

 impressed with the idea that the figures and descriptions of the species 

 of Cymhidia extant were not reliable ; and having had an opportunity 

 of examining some specimens taken in the Indian Ocean, he found 

 that such was really the case. 



In the natural position of the animal the toe of the hyaline slipper 

 of Cymhulia should be taken as posterior, and the broadly notched 

 heel as anterior. Both animal and shell are reversed in Mr. Adams's 

 figure of Cymbulia proboscidea, but this is, after all, an error of less 

 importance than that in De Blainville's figure, in which, although 

 the shell is represented in its proper position, the animal is reversed. 

 A pair of eyes are also given in a position where ears alone would 

 be possible, while there is no more evidence of the existence of eyes 

 in Cymbulia than in any other genus of Pteropods. The notion of a 

 ventral connecting lobe between the fins is a mistake, though these 

 organs are connected above and behind so as to form a broad, con- 

 tinuous plate. 



Molluscoida. 

 a. Tunicata. 



Development of Social Ascidians.f— Dr. O. Seeliger finds in 

 the Salpidse, Doliolidae, and Anchinia various modifications of a true 

 alternation of generation which, as a developmental cycle, was peculiar 

 to their common stem-form. This form was free-swimming and 

 developed ventral buds, just as now the tailed Doliolum-laTva 

 developes the rosette-shaped organ. Primitively the solitary forms 

 may have passed over their capacity to dcvelopo generative products 

 to the buds, but very soon the whole of the embryonic material 

 appears to have passed into the buds, which had probably a somewhat 

 c<^>mplicated structure. The developmental cycle of tl;o Pyrosoma- 

 tidse is also to be referred to the budding of the same free-swimming 



• Proo. Roy. Soc.. xxxviii. (1885) pp. 251-3 ( 1 fig.) 



t Jenaihch. Zf-itfichr. f. Nntiirwifis., xviii. '^1885) pp. 528-06. 



