place nearly at right angles. Owing to this, a clear 

 occipital projection is seen from the outside. Baer con- 

 sidered the bends of the brain to be the result of its 

 intensive growth, which the skull cavity has no time to 

 follow. The organs of sensation develop as in birds. 



The primary kidneys, similar to those in birds, appear 

 and disappear. Toward the outside the constant kidneys 

 originate; at first they are stretched in length, then they 

 become rounded and move away from the vertebra than in birds. 



The transformations of the genital system are very 

 complicated. The genital glands have the form of spindles 

 in the internal sides of the primary kidneys; in the external 

 convex edge of the primary kidneys, simultaneous with the 

 genital glands, a thread-like conducting canal appears. 

 This is the future seminal duct or oviduct. In the cloaca, 

 two lateral folds form, which then unite. They separate 

 the rectum from the part which gives rise to the allantoic 

 sac. Besides this, the external orifice divides into two 

 parts for the formation of perineum. Further, the genital 

 glands become rounded, and by histological separation in 

 males the canalicules are developed, and in females the 

 Graafian follicles later develop. The conducting genital 

 ducts in females are widened and supplied by an orifice in 

 the abdominal cavity; the uterus and vagina develop later on. 



Baer described in detail the development of the external 

 genital parts, cavernous bodies, urethra, uterus and vagina, 

 and also the descending of testicles from the abdominal 

 cavity to the scrotum. 



Baer mentioned little about the development of the 

 diaphragm, noting that he could not give it special attention, 

 He did, however, establish the facts of gradual backwards 

 displacement of the diaphragm, of elongation of the embryonic 

 thoracic cavity, and of the growth of muscles from the wall 

 of the body. Baer described the serous membranes briefly, 

 whereas he described development of the mesentery in more 

 detail. He described its displacement during the formation 

 of intestinal loops and mentioned the turning of the stomach 

 and the origin of omentum. 



414 



