1885.] 



Ovum of the South A frican Peripatus. 



241 



4. The last form I have to describe is the spindle form. It was met 

 with in an ovum of two segments. 



The spindle is of enormous size (distance between the poles 0*06 mm.).. 

 The protoplasmic fibres composing it are absolutely the same in 

 appearance as the rest of the cell protoplasm. The chromatin is 

 present in a very condensed form (i.e., deeply staining) as a number 

 of bent rods at the equator of the spindle. Around the poles of the- 

 spindle the protoplasmic reticulum is arranged in a radiate fashion. 

 The spindle appears not to be composed of simple fibres running from 

 pole to pole, but of the ordinary reticulum, the meshes of which are 

 very much elongated in a direction parallel to the long axis of the- 

 spindle. 



The facts which are most clearly brought out by the above obser- 

 vations, and about which I have no doubt, are — 



1. The continuity of the nuclear reticulum with the extra-nuclear 

 reticulum in form 3 (and almost certainly in forms 1 and 2).. 



2. The similarity in structure and continuity between the so- 

 called fibres of the spindle in form 4 with the surrounding reticulum ; 

 and the conclusion I have drawn from my observations is that the 

 nucleus of the fertilised ovum of Peripatus differs from the cell proto- 

 plasm only in the manner in which the so-called chromatin contained 

 in the protoplasmic mesh work (both of nucleus and rest of ovum) 

 behaves. In the nucleus it varies from a state of diffusion through 

 the reticulum to a state in which it is condensed into, the chromatin 

 masses of form 1. 



In the subsequent stages of segmentation, the nucleus gradually 

 becomes smaller until at the close of segmentation it has an oval 

 form with a long diameter of 0*016 mm. It now presents the features 

 described by Flemming and other observers in the nuclei of the 

 salamander. I have seen all through the development of Peripatus 

 after segmentation most of the stages figured from the salamander. 



During segmentation the nucleus generally has the third form above 

 described: I have never seen it in a spherical, and only once in a 

 spindle form. I conclude that these forms if they occur are very 

 rapidly passed through. 



The Segmentation. 



I have already described this in a general manner in my communi- 

 cation of May last, and with figures in the " Quarterly Journal of 

 Microscopical Science " of July last. 



I then stated that the endoderm cells were connected with each 

 other by processes ("Quart. Journ. Micros. Sci.," xxv, Plate 31, 

 fig. 8). I have now the following facts to add : — 



1. The so-called endoderm cells are at first without a distinct 

 nucleus, they do not get a nucleus until just before the gastrula stage. 



r 2 



