OOGENESIS AND EARLY EMBRYOLOGY ASCARIS 537 



has been done on the development of the oogonia of Nematodes. 

 Marcus ('06) in his work on A. canis (?) passes this stage by with 

 only a remark on the smallness of the elements, and the state- 

 ment that the plasmosome detaches itself from the chromatic 

 mass, which then breaks up into chromosomes having a trans- 

 verse constriction. In another dog ascarid, A. marginata, 

 Lukjanow ('89) figures the 'stem cell', from which the oogonia 

 originate, and the oogonial divisions as being niitotic in charac- 

 ter. In his preparations tiJie individual chromosomes were dis- 

 tinct and of thread-like character during these divisions. Kult- 

 schitzky ('88 c), also working on A. marginata, does not figure 

 the oogonial stages. 



Descriptions of the oogonial stages of A. megalocephala are 

 much* more numerous and complete. Hertwig ('90) shows that 

 the chromosomes are formed from continuous spireme threads, 

 which have arisen by the congregating of chromatic granules 

 imbedded in a linin network. These chromosomes occasionally 

 show a longitudinal splitting as a forerunner of their future 

 plane of division. Brauer ('03), on the contrary, finds that in 

 the spermatogonia the spireme thread is never continuous, but 

 that each chromosome arises from a separate thread. Edwards 

 ('10) maintains that in thirty-two per cent of the oogonia studied 

 by him, the single idiosome is found as a separate body. In 

 opposition to this view, Boveri ('11) and Frolowa ('12) think 

 that the idiosome is generally attached to the end of an autosome, 

 and exists only occasionally as a separate chromosome. Geinitz 

 ('13) believes, as also does Kautzsch ('13), that the idiosomes, 

 as well as the chromosomes, are multiple structures. Tretja- 

 koff ('04 b) finds that the chromatin of the spermatogonia first 

 exists as a central mass, which then breaks up into fine threads. 

 These, after assuming a peripheral position, shorten into thick, 

 rod-like bodies. By a process of parasyndesis, two of these 

 bodies conjugate to form a true chromosome. 



The nuclear wall in the case of A. megalocephala consists 

 (Van Beneden, '83) of a layer of linin containing microsomes. 

 The same method of formation of the nuclear membrane is re- 

 ported by Goldsmith ('16) for Pselliodes cinctus. My own work 



