and Laboratory Methods. 2193 



CYTOLOGY, EMBRYOLOGY, 



AND 



MICROSCOPICAL METHODS. 



AGNES M. CLAYPOLE, Throop Polytechnic Institute. 



Separates of Papers and Books on Animal Biology should be sent for Review to Agnes M. Claypole, 



55 S. Marengo Avenue, Pasadena, Cal. 



Eycleshymer, A. C. The Formation of the The author presents some observations 

 Embryo of Necturus with Remarks on the , , . ^ , • ^ c ^i 



Theory of Concrescence. Anat. Anz. 21: ^nd conclusions obtained from the 



341-353. 1902. study of the eggs of Mr^urus and other 



Amphibians relative to the theory of concrescence. From previous work on 

 Rana, Acris, Bufo and Amblystoma, he concluded as follows : The cephalic end 

 of the embryo is formed at the upper pole of the egg ; the greater part of the 

 posterior half is formed about the blastopore ; the posterior end of the embryo 

 is formed by a coalescence of the lateral portions of the blastoporic margin. 

 Hence the greater part of the embryo arises in the darker hemisphere by 

 differentiation in situ, and not by concrescence. A series of experiments on 

 the eggs of Necturus gives the result that much more of the embryo is formed 

 by concrescence than in the other Amphibia. The explanation of this lies in 

 the fact that the eggs of Necturus, containing much more yolk material, tend to 

 develop more meroblastically than do any other amphibian eggs. This causes 

 a much larger proportion of the embryo to be formed by coalescence of the 

 lateral margins of the blastopore. With the still greater amount of yolk found 

 in most Teleosts, still less embryo is formed in situ and in Elasmobranches and 

 birds where the yolk mass is greatest, concrescence gives rise to by far the 

 greatest part of the embryo, only a very limited region at the cephalic end being 

 formed by differentiation in situ. This indicates that the primitive method of 

 embryo formation is by differentiation in situ, concrescence being a secondary 

 process, which has progressed pa7-i passu with increase of yolk material. The 

 methods employed were puncturing the eggs at various stages of development, 

 and observing where the scar produced was placed in regard to the body of the 

 forming embryo. One series in the second cleavage stage and two in the early 

 gastula stage were punctured, and on those that developed the above observa- 

 tions were made. Some difficulty was experienced, due to the easy removal of 

 the exovates and the ease with which such large ones can be formed as to 

 interfere with the normal development of the eggs. This makes Necturus a less 

 favorable form for experimentation than most of the amphibia. e. j. c. 



Nusbaum, J., and Machowski, J. Die Bildung -pj^g authors have taken up the problem 

 der concentrischen Kbrperchen und die 



phagocytotischen Vorgange bei der Involu- of the structure and formation of the cor- 



tion der Amphibienthymus nebst einige puscles of Hassal in the Amphibian 

 Bermerkungen iiber die Kiemenreste und 



Epithelkorper der Amphibien. Anat. Anz. Thymus and have traced the processes 

 21 : 1 10-127, figs- 1-5. i9°2. these bodies undergo in their degenera- 

 tion, especially the part played by leucocytes in these changes. Much 

 difference of opinion exists as to whether the corpuscles are of epithelial or of 



