MUSEUM OF COMPARATIVE ZOOLOGY. 237 



clothed in a layer of soluble protoplasm (Sckleim) which takes the place 

 of a membrane. It possesses an envelope (HiiUe), it is true, but it is 

 not membranous, — it is simply one of thickened protoplasm. For 

 this reason the author cannot agree with those who do not admit the 

 existence of any envelope. 



The observations of Warneck on the early changes of the egg in 

 Lymnaeus and Limax were far more extensive and accurate than those 

 of his predecessors ; they were, in fact, in advance of most of the con- 

 temporary studies in other branches of embryology, and came near 

 anticipating some of the more important discoveries of the present 

 decade. His paper (1850) marks approximately the beginning of a 

 reversion of ideas as to the total disappearance of the Purkinjean 

 vesicle which had been dominant since its discovery in 1825; and, if I 

 have not mistaken his meaning, Warneck may fairly be reckoned among 

 the first who entertained doubts as to a complete dissolution of this 

 structure. 



It must be admitted, however, that the reputation of Johannes 

 Miiller was the sufficient cause for the more general reception of new 

 views on this point in embryology. Although Warneck's paper ante- 

 dates by two years that of the latter author, there can be little question 

 that the influence of his writing has been inconsiderable when compared 

 with that of Muller.=* 



According to Warneck ('50, pp. 114, 115) one discovers within the 

 yolk-mass of the impregnated egg a clear spot, which is due to a cavity 

 filled with an albuminous fluid as clear as water, and containing no 

 elementary corpuscles, such as occupy the yolk. This clear spot occu- 

 pies exactly the place of the Purkinjean vesicle. No distinct contour is 

 observable, the transparency of the spot diminishing toward the periphery, 

 so that it gradually merges into the yolk-mass. Its position is central. 



Although not thus sharply formulated, I think there can be no doubt 

 that Warneck believed the " clear spot " to be the Purkinjean vesicle 

 metamorphosed by the disappearance of its membrane and its numer- 

 ous germinative dots (p. 177). 



* Among others, Hermann Fol has recently called attention to this paper by War- 

 neck, whose work he estimates very highly. While one cannot fail to admire the 

 generous spirit which prompts this opinion of the merit of Warneck, it is much more 

 difficult to subscribe to the interpretation which Fol puts upon certain portions of his 

 paper. 



Brandt ('77^ pp. 593, 594) has made use of the studies of Warneck to corrobo- 

 rate his own observations on the amoeboid nature of the germinative vesicle, in a 

 manner which appears to me unjustifiable, as will presently be shown. 



