MUSEUM OF COMPARATIVE ZOOLOGY. 177 



commence after a part of these maturation changes have already tran- 

 spired. These three series of events will be treated in the order men- 

 tioned, as that is substantially the order of their occurrence in time ; 

 it should be mentioned, however, that they are not strictly and com- 

 pletely consecutive, for each series of changes is still incomplete at the 

 beginning of the next following, — there is, as it were, an overlapping 

 in time, — and for this reason it will be less advisable to follow the strict 

 chronological, than the physiological order as above indicated. 



As far as regards what may be observed on the living egg, the very 

 accurate studies of Nicholas Warneck, though made as long ago as 

 1850, leave very little room for additions. 



It was some time after my first studies (middle April — middle May, 

 1877) on Limax were ended before the opportunity was afforded for an 

 examination of the literature on the development of pulmonates, which 

 was entirely inaccessible to me at the time I was making the observa- 

 tions. Among other references in Bronn's Die Klassen und Ordnungen 

 des Thier-Reichs was that which first directed my attention to this valu- 

 able paper by Warneck, hitherto unknown to me even by title. I was 

 temporarily deterred from publishing my studies by the fact that this 

 observer had already published so truthful and complete an account of 

 the development in the case of a slug very nearly related to the one 

 which had formed the basis of my investigations. There were still 

 some points (more especially in the stages of segmentation, which will 

 fall outside the limits of the present paper) in which my observations 

 were at variance with those of the Russian naturalist. It was in part 

 these matters of disagreement, but more especially the influence of the 

 recent writings of Butschli, Hertwig, Fol, and others, which determined 

 me, early in 1878, to renew my observations at the first opportunity, and 

 to address particular attention to the phenomena to be observed before 

 and during the first segmentation. I was able to devote only a few days 

 to this study in Cambridge, during the latter part of June. The most 

 of the observations were made at Fredonia, in August, 1878. 



I. Maturation. 



In eggs examined directly after their deposit the vitellus appears 

 as a spherical mass of a slightly yellowish or brownish tint, with per- 

 fectly clear, sharp outline, about 0.125 mm. in diameter. It has greater 

 density than the surrounding albumen. Its opacity is occasioned by 

 an immense number of granulations, varjdng in size. Part of these 



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