248 Papers from the Department of Marine Biology. 



It was very noticeable that only the plasmosome was moved and 

 that the other structures in the nucleus appeared to maintain their 

 positions. In some few cases a few of the chromatin bodies seemed to 

 be moved from their position with relation to the other bodies in the 

 nucleus, but for the most they were not disturbed. Figure 21, plate 5, 

 shows one of these cells. 



An interesting cytoplasmic change took place in this specimen, which 

 may be mentioned here. The whole nucleus, as well as the cell itself, 

 appeared in a number of cases to be slightly flattened by the pressure, 

 and as a result a circular equatorial channel filled with lymph-like 

 fluid appeared to girdle the nucleus. From this belt-like channel a 

 series of radiating lines of some form of non-staining cytoplasm pass 

 out. They are not fibrillar in nature and the whole structure simulates 

 superficially a centrosome. This torpedo was of large size. 



In the next gravity experiment, on torpedo No. 20, a force of 601 

 times gravity w T as applied for a period of nearly half an hour. The 

 control showed 90 per cent ventral orientation, as might be expected 

 in so large a fish (37 cm.). As has been related in the account of the 

 experiment, the force was applied in a ventro-dorsal direction, with the 

 result that not only the plasmosome but all of the chromatin bodies 

 were thrown against the dorsal wall of the nucleus. The plasmosome 

 lay nearest to and against the nuclear wall. The chromatin bodies 

 \&y in a mass with its level inner edge forming a secant of the circular 

 outline of the nucleus. It was noticeable that the chromatin be 

 showed no signs of flattening and that the central body or karyosonie 

 had not moved through the perichromatin; the whole structures (ci. 

 matin bodies) thus appear to be bodies of considerable firmness. Nor 

 v:ere the entire chromatin bodies very closely packed; they still retained 

 their round outlines. 



A question suggests itself here: does the plasmosome yield to in- 

 creasing centrifugal force first because it is not so strongly held as the 

 chromatin bodies or because it is actually heavier? This can be 

 answered, I think, from an inspection of the control or normal material. 

 In such sections (see fig. 2, plate 1, and figs. 4 to 9, plate 2) one can 

 easily see that the plasmosome is connected with all parts of the nuclear 

 wall by a considerable number of strands of loosely woven fibrils and is 

 evidently held in its position in the nucleus by as strong if not a 

 stronger set of structures than are the chromatin bodies. 



The last experiment of the gravity kind to be considered is that 

 performed on torpedo No. 4, in which a force of 828.5 times gravity 

 was applied by centrifuging a portion of the electric lobes in a direction 

 at right angles to the natural force (anterior-posterior). The propor- 

 tion of ventral orientation in the control was 70 per cent and with the 

 large artificial force applied the entire number of chromatin bodies as 

 well as the plasmosome were thrown against the posterior Avail of the 

 nucleus. 



