No. 633] 



XEOTEXY 



353 



cells goes as far as the formation of the maturation divi- 

 sion in first year larvae, and ripe spermatozoa in second 

 year animals. This is of course due to the extraordi- 

 narily long larval period. In Rana temporaria and Rana 

 esculenta the larval maturation changes apparently go 

 only up to and including the pachytene stages before de- 

 generation sets in. In Bufo, the precocious ripening of 

 the sex cells is confined entirely to the cells of Bidder's 

 organ and continues up to the pachytene stage before 

 growth begins. 



The male larvae of Rana catesbiana undergo two dis- 

 tinct seasonal maturation cycles as larvae. The first oc- 

 curs in young animals 45-60 mm. total length, despite the 

 fact that the germ gland is in an extremely undifferenti- 

 ated condition. The germ cells develop normally through 

 the leptotene, pachytene, diplotene and tetrad formation 

 stages, but invariably degenerate and go to pieces dur'mi: 

 the late metaphase or early anaphase of the first matura- 

 tion division. The centrosomes fragment and the spindle 

 apparatus is aberrant. There are no second maturation 

 divisions, though occasional giant spermat id-like struc- 

 tures may form by the growth of axial filaments from the 

 centrosomes of first spermatocytes. The cells of the first 

 larval maturation cycle degenerate. Through active 

 mitotic division tic few primary sprnnatou-onia scattered 

 throughout the gland give origin to those cells which 

 later undergo the second larval sexual cycle. This sec- 

 ond cycle occurs near the end of larval life, i.e., usually 

 about two years after hatching. Oddly enough the sec- 

 ond maturation cycle is normal, and gives rise to func- 

 tional spermatozoa in the larvae, though the efferent ducts 

 of the testes are not yet fully formed. The germ cells 

 and tetrads of the first sexual cycle are aberrant in size 

 and character, those of the second cycle are normal in 

 every way. 



The diploid chromosome number of the larvae is twen- 

 ty-eight, the haploid number is fourteen. There is no 

 evidence of an accessory chromosome. 



