82 bulletin: museum of comparative zoology. 



Instead of considering that we have here a regular revokition of the 

 nucleus, it seems to me more reasonable to suppose the variation in 

 the position of the point of attachment in the earlier stages to be due 

 to the mutual pressure of surrounding cells. The interzonal body, 

 which is the criterion used to distinguish the distal pole, invariably 

 lies in the part of the cell containing th:^ greatest amount of cytoplasm, 

 and the shape of any c(.41 is certainly largely determined by the pres- 

 sure of surrounding cells. It would, therefore, seem only reasonable 

 to suppose that the relative positions of the nucleus and interzonal 

 body might be considerably influenced in this way. The revolution 

 of the nucleus in some cases would, th'>n, be simply a readjustment 

 in the cell to a more or less definitely fixed polarity which had been 

 temporarily lost. 



In the following stage (e) the chromatin granules (Plate 2, Fig. 34), 

 which are distributed along the spireme threads, divide so that each 

 loop shows more or less distinctly a longitudinal split. It should be 

 clearly understood that this splitting does not extend to the linin, which 

 now forms a flattened ribbon like structure, in which the paired chro- 

 matin granules are imbedded. This stage imdoubtedly corresponds 

 to the split spireme of authors. I believe this double series of chro- 

 matin granules to be formed by the splitting of the single series of 

 granules of the preceding stage, rather than by a side to side union of 

 two distinct threads, as has been held by a number of recent writers 

 to be the case in other forms. Long and careful study of a large num- 

 ber of cells in this and preceding stages has convinced me that there 

 is little evidence in this species (or in other Orthoptera) of a side to side 

 union of the spireme threads. Occasionally during the preceding 

 stage two threads can be seen lying parallel for a short distance, but 

 if carefully followed they can in almost all cases be seen to diverge 

 again. This, combined with the fact that such structures are com- 

 paratively rare, has convinced me that they are only accidental . More- 

 over, in stage e part of the chromatin granules along a given thread 

 may be single while others are double. The single granul-^s are 

 usually elongated transversely to the thread as though preparing to 

 divide into two. Of course it may be argued that those granules are 

 formed by the fusion of two originally distinct granules, but there is 

 little to support such an interpretation, since th^re is no evidence that 

 the longitudinal split later becomes obliterated by the fusion of the 

 halves. However, the whole question will be taken up later, in a dis- 

 cussion of the literature, where it can be considered to greater ad- 

 vantage. During stage e the polar arrangement of the spireme is 



