(pp. 24-31). In a section about UBER ENTWICKLUNGSGESCHICHT 

 (II, 11 bb) , also in detail, he reviewed the transformation of 

 cerebral vesicles of the embryo into the part of the definitive 

 brain as in Cyprinus blioca, and as also in other carps (Cyprinui 

 erythrophthalmus) and cartilaginous fishes. 



Baer gave limited information on the digestive system. 

 The oral orifice opens at the end of the first day after 

 hatching. The intestinal canal up to the fifth day is very 

 wide, completely direct and easily distinguished from the yolk 

 sac, which is diminished. The mesentery appears later on (at 

 the beginning, the intestine is adjacent to the spinal column); 

 however, its development undoubtedly takes place exactly as in 

 birds and mammals. 



More briefly, Baer mentioned the development of the 

 excretory system, noticing that kidneys of fish do not undergo 

 that transformation which is characteristic of the higher 

 vertebrates. In connection with this, the corresponding 

 reconstruction of the circulatory system does not take place. 



Later Baer gave a fluent description of the development 

 of the paired extremities and unpaired fins. He noted that 

 at the beginning, the unpaired fins in all fish, regardless of 

 the future structure of fins with dense edgings, are situated 

 from the back through the tail to the ventral side. Then 

 the fringes are broken into as many parts as there are 

 separated unpaired fins in the given fish. Between these 

 regions the fringes disappear, and in the remaining fins 

 cartilaginous or bony arms develop. 



The development of the swimming sac was given special 

 detailed attention by Baer in separate works (see footnote 8) . 

 The posterior swimming vesicle of carp fish, according to 

 Baer, is analogous to the underdeveloped lung because, like 

 the latter, it arises from the protruding anterior region of 

 the digestive canal . In hatching embryos there are no traces 

 of the swimming vesicle and only near the end of the first 

 day in the material, condensed in nitric acid can two pro- 

 trusions be seen, one from the back and the other from the 

 ventral side, each of them about 0.1 inch in size (Figure 32, 

 24) . On the second day the dorsal protrusion acquires a 

 finger- like form and is elongated backwards (Figure 32, 25) . 



434 



