52 C. 0. Whitman 



autour du noyau du germi gène et par là les germes sont rejetès à la 



Peripherie, pnis éliminés Des qu une première generation a été 



ainsi expulsée, il s'en forme un seconde ; ces nouveaux germes naissent 

 et se développent de la méme manière que les premiers ; ils sont ex- 

 pulsés à leur tour pour étre remplaeés par une troisième sèrie, et ainsi 

 les gènèrations nouvelles refoulent peu à peu, de dedans en dehors, les 

 générations plus anciennes. Il en rèsulte des couches coneentriques de 

 germes d'autant plus volumineux qu'ils sont plus loin du centre.« 

 (1, p. 52^ — 53.) Now ali this applies to wliat comes after the stages rep- 

 resented in fìg-s. lOS and 109. These stages are reached by repeated 

 division of the celi ni in figs. 104, 105 ; and this celi is not therefore 

 identical with the centrai celi, or germogen seen in fig. 109 and later 

 stages. The two-cell stage is seen in figs. 106 and 107, g. I bave seen 

 stages of three, five, six (fig. 108), and teu to twelve cells [fig. 109). 

 I bave not succeeded in tracing the origin of the germogen, i. e. I can 

 not say precisely bow early it appears. I bave not been able to recog- 

 nize it earlier tban the six-cell stage, fig. 108 ; and in tbis case I could 

 not clearly distinguish its boundary. In fig. 109, taken from the same 

 individuai, its outline is quite distinct and its nucleus very conspicuously 

 different from the nuclei of the peripberal cells. It evidently arises quite 

 early, and is one of the products of the divisioif of the celi m. It is also 

 certain tbat the peripberal cells seen in 1 08 and 1 09 continue to multiply 

 by division as late as stage HO, and probably stili later. By tbe time 

 stage 109 is reached, or soon after, tbe germogen becomes tbe seat of 

 endogenous cell-formation. How tbe first cells arise w^itbin tbe germ- 

 ogen, I bave not been able to ascertain ; but it is probable tbat they 

 originate in tbe first instance by a division of tbe nucleus of tbe germ- 

 ogen, as is the case in tbe vermiform embryo. Tbe successive gènèra- 

 tions might then arise in tbe same way, or, more probably, by division 

 of tbe primary germ-cells. 



Althougb my observations on the origin of tbe Infusorigen leave a 

 number of important points undecided, so much is at least certain, tbat 

 it does not arise from eudogenously formed cells, but from a single celi, 

 tbrough a process of division analogous to, if not identical with, tbat of 

 cleavage. I am unable to understand tbis fact on any otber bypotbesis 

 tban tbat tbe Infusorigen represents an individuality , of similar rank 

 with tbe Gastrula of tbe vermiform embryo. Stili I am not fully per- 

 suaded tbat this Interpretation is correct. The important point wbich 

 remains to be cleared up is tbe origin of tbe germ-cells witbin tbe germ- 

 ogen. If tbey arise in tbe same way tbat germ-cells arise in tbe axial 



