GERM CELLS IN ASCARIS INCURVA 75 



contraction or synizesis (McClung '05) during which the thick 

 threads are formed — zygotene stage; the thick threads persist 

 for a considerable period — pachytene stage; they are early or 

 even throughout of double nature and later split lengthwise — 

 diplotene stage, lengthening and twisting about one another as 

 this occurs — strepsitene stage. A diffuse, unanalyzable stage 

 enters hel^e which is followed by the prophases of the maturation 

 division. Of these stages, the pachytene nucleus does not so 

 clearly show the looping, characteristic of many forms, and the 

 strepsitene stage as it merges rapidly with the 'diffuse' condition 

 is less readily identifiable; but the series is essentially like that 

 established elsewhere. 



No description clearly showing this seriation in Ascaris has 

 hitherto appeared but a critical study of the figures of Hertwig 

 ('90), Brauer ('93) and Tretjakoff ('05) indicates that certain 

 conditions observed by these writers may be correlated with 

 similar conditions in Ascaris incurva so that it is highly probable 

 that the same complete seriation also exists in all species of 

 Ascaris. 2 DeSaedleer ('12) has made a detailed study of the 

 oogenesis of Ascaris megalocephala and correlates his results 

 with this same scheme of seriation but his figures emphasize 



- That Ascaris megalocephala need not be considered as an exceptional 'case 

 in regard to the growth stages may be seen by a comparison of conditions there 

 observed with those in Ascaris incurva. The difficulty of correlation has resulted 

 in part from the fact that the leptotene and synizesis stages occur early near 

 the inner end of the long gonad while the cells are quite small. 



Hertwig ('90), plate 2, figure 5 and Tretjakoff ('05), figures 7, 78, 79 describe 

 a condition without doubt homologous to the late leptotene or early synizeses 

 stage of A. incurva. The figures suggest a fine meshwork of threads and a plas- 

 masome at one edge of the mass showing the same polarization that is found in 

 these stages only, in Ascaris incurva. Hertwig mentions at this stage the ab- 

 sence of a nuclear membrane and it is true that in A. incurva this structure is 

 recognizable with difficulty. Tretjakoff, only, describes a full contraction 

 figure showing looping threads (fig. 80) but does not recognize its significance, 

 identifying a later stage as comparable with this condition in other forms. Hert- 

 wig, plate 1, figure 8, Brauer, figures 15 to 21 and 67 to 81, and also Marcus ('06), 

 in Ascaris canis, figure 2, b. c, d, show the type of pachyteme stage characteristic 

 of the genus and comparable with that in A. incurva, figure 11. Tretjakoff's 

 figure 84 may also be of this same condition but both he and Marcus compare 

 this with the synizesis of other forms, as there exists a tendency for chromatin 

 to mass about the plasmasome, but it certainly is not that condition which so 



