SMALL WOOD : MATURATION OF HAMIXEA SOLITARIA. 281 



rod-shaped chromosomes before the first division occurred, had the egg 

 been left to develop normally. However, the tripartite form may some- 

 times be retained until a comparatively late stage (Plate 5, Fig. 25), 

 In Figure 19 (Plate 4) is shown one chromosome of a form that occurs 

 very often at this stage, — four small masses of chromatic substance con- 

 nected by a slender thread of chromatin. Chromosomes of this kind 

 assume the rod-like form before division, and are always unusually long 

 and thin. When we compare this form with the conditions seen in 

 Figure 20, it seems probable that we have here a transition between the 

 tripartite chromosome and the simple rod. Two of the chromosomes in 

 Figure 20 indicate a possible relation to chromatin rings in tetrad for- 

 mation, for they look as if they were about finishing a longitudinal 

 division, the form being similar to that described by Griffin ('99) for 

 Thalassema and Zirphea ; but from the changes which follow, it is 

 probable that this is not a case of longitudinal splitting, for in the first 

 cleavage the chromosomes divide transversely (Fig. 29, Plate 5). The 

 chromosomes are at first connected by conspicuous chromatin threads, 

 which become delicate, lose their capacity for stain, and finally disappear. 

 The migration of the chromosomes toward the poles of the spindle takes 

 place in the usual manner (Figs. 26-28). 



(II.) Second Matdkation Figure. 



Considerable time was spent in attempting to bring into one series all 

 of the stages observed in Haminea. The idea that two or more distinct 

 processes might take place normally was thought to be improbable. 

 Additional preparations exhibiting the second maturation figure were 

 made, but the same diff"erences were still found to exist. After further 

 study it was found possible to bring the vai'ious conditions into two 

 distinct series. The difterences between the two are so great that they 

 might well belong to distinct varieties of Haminea ; indeed, one might 

 question whether the eggs were not actually from different species, were 

 it not for the fact that they were all laid, while under observation in the 

 aquaria, by animals all of whose external characteristics pointed to their 

 being of a single species. To the possible view that artificial conditions 

 may have caused the difference, the reply can be made that the same 

 diff'erences have been observed in eggs collected from the regular breed- 

 ing-places in the sea. 



The two processes occur with about the same frequency, but all the 

 eggs in one capsule follow either one method or the other. Any division 

 of these processes into successive stages must be more or less arbitrary, 



