tracing the embryological literatures. Therefore, the 

 investigations of Shvani were unknown to him (376) . 



(1QQ) In the footnote, Baer proved his suggestion to 

 replace the name "allantois" by the term "urine sac". It 

 is necessary to admit that both the old name — allantois and 

 that of Baer — "allantoid" which corresponds to the form of 

 embryonic organ only in hoofed mammals, or Baer's name — 

 urine sac were successful. The urine sac, i.e. the reservoir 

 of products of excretion, as allantois is in Saurops-ida and 

 in a few mammals (namely in hoofed), while in other mammals 

 it possesses an underdeveloped cavity or even, is quite absent. 



(101) In the note to the place of the Russian work of 

 Baer, P. G. Svetlov drew attention to the importance of the 

 mentioned idea of Baer. It was totally fair to regard it as 

 containing the rudiment of the theory of embryonic plates as 

 parts of general vertebrates. Moreover, this generalization 

 arises in the process of embryonic development and can be 

 established only during the study of the latter one. In the 

 same note, it was stated, that layers, noticed by Baer in 



the body of vertebrates, did not, strictly speaking, correspond 

 to embryonic plates and that Baer was not in situation "to 

 complete his outstanding retrospective analysis of organs of 

 the formulated animal up to the stage of "primary separation", 

 i.e. to the embryonic plates" (Note 34, p. 459) (381) . 



(102) This place of the Baer article is difficult to 

 understand, as the translators of the second volume of "History 

 of animal development remarked. P. G. Svetlov, made an attempt 

 to interpret the very laconic stated ideas of Baer. The 

 interpretation suggested by him (note 63, page 464) is extremely 

 probable, but cannot withstand a complete proof (390) . 



(103) The aspiration for widening the field of the 

 comparative-embryological investigations prompted Baer to use 

 the necessary materials so as to strengthen the researches. 

 In the work about the development of tortoise (see footnote 

 on page 405) , Baer described the difficulties to which the 

 obtaining of their eggs was connected. In environs of 

 Kenigsberg, tortoises were absent. He asked for tortoise eggs 

 from Litva. "If the eggs died on the way, or females carried 

 infertile eggs, I did not obtain, in all cases, desirable results 



640 



