COLD-BLOODp]D VERTEBRATES 



1061 



tliere are two oviducts and two ^'aJ^a def- 

 erentia. When a body length of 100 nnn. is 

 reached, either the testicuUir component 

 and vasa deferentia degenerate, or the ovar- 

 ian conii^onent and the oviducts disajipear 

 (Kinoshita, 1936). 



Ainphihians 



Sec chapter by Burns. 

 Reptiles 



Probably the first i)ublislied observations 

 on the embryology of the reproductive sys- 

 tem in the turtle were those of Rathke 

 (1848). Risley has summarized the sub- 

 sequent literature on the subject and has 

 carefully analyzed the origin of the germ 

 cells (1933b) and the embryology of the 

 reproductive system (1933c) in Sterno- 

 therus odoratus, the musk turtle. He rec- 

 ognized three stages in gonadal de- 

 velopment — indifferent, bisexual, and 

 differentiated. During the indifferent phase 

 the primitive germinal epithelium, a spe- 

 cialized area of peritoneum investing the 

 ventromedial surface of each mesonephros, 

 dorsally proliferates sex cords containing 

 germ cells. Stromal elements grow between 

 the epithelial sex cords. The gradually 

 thickening mass of tissue thus formed is 

 known as the genital ridge. Extension of the 

 epithelial elements of the sex cord beyond 

 the gonad and to a nearby Malpighian cor- 

 puscle in the mesonephros marks the estab- 

 lishment of the rete cord connection. 



In the bisexual period there is a further 

 proliferation of the germinal epithelium 

 and its germ cells to form an investing 

 cortex. Internal to the latter is a medulla 

 composed of the original sex cords and their 

 gametes. Cortex and medulla are both well 

 developed, and all embryos at this stage 

 also have mesonephroi (potential epididy- 

 mides), mesonephric ducts (potential vasa 

 deferentia), Miillerian ducts, and phalluses. 

 This bisexual condition, sometimes referred 

 to as juvenile or rudimentary hermaphrodi- 

 tism, persists for a relatively long time. 

 Late in embryonic development, morpho- 

 logic sex differentiation ensues as a third 

 stage. In the male, the medullary cords 

 begin to acquire lumina and to become 

 seminiferous tubules and the cortex and 



Miillerian duct begin to regress. In the fe- 

 male, the cortex develops further, the med- 

 ullary cords regress to connective tissue 

 strands, and the growth of the phallus is 

 checked. It must be emphasized, however, 

 that at hatching heterosexual vestiges are 

 still conspicuous. 



The development of the reproductive 

 tract in most other reptiles is also relatively 

 slow as compared to that of higher verte- 

 brates. The process may in fact never really 

 be completed, so that the adult frequently 

 or regularly retains definite heterosexual 

 remnants, e.g., a vestigial mesonephros in 

 the female and a part of the Miillerian 

 duct in the male. 



Risley's account for the turtle in general 

 confirms Braun's early (1877) account of 

 the development of the reproductive system 

 in lizards and snakes (chiefly Lacerta, 

 Anguis. Tropidonotus, and Coronella). 

 Mihalkovics' (1885) excellent study (chiefly 

 of the lizard) added important information. 

 He reminds his readers, for example, that 

 Braun "was struck by the proximity of the 

 adrenal anlage to that of the gonad in rep- 

 tiles ... so that one would be led to think 

 of a relationship between the two struc- 

 tures." This is in reference to the fact that 

 the adrenal cortex takes origin from spe- 

 cialized epithelium lying between the root 

 of the mesentery and the germinal epithe- 

 lium. The anlage of the adrenal cortex 

 (medial) and the anlage of the genital ridge 

 (lateral) i^roliferate epithelial cords dor- 

 sally at about the same time. Actually, it 

 is diflficult to determine the dividing line be- 

 tween the two anlagen at this early stage 

 except on the basis that the germ cells 

 normally are confined to the develop- 

 ing gonad. This physical continuity in 

 the embryo is sometimes overlooked, but 

 is of interest in view of the demonstrated 

 ability of the adult mammalian adrenal 

 cortex to produce sex hormones, an ability 

 which may well be shared by some of the 

 lower vertebrates. Other accounts are those 

 of Hoffmann (1889), Peter (1904), Simkins 

 and Asana (1930), and Forbes (1956). 



Regamey (1935) mentions a male Lacerta 

 embryo of advanced development which 

 retained both oviducts. Dantchakoff (1938) 

 describes male and female lizard embryos 



