1885.] On the Fertilised Ovum of Peripatus. 239 



Arthur Schuster, Ph.D. ; Lieutenant- General R. Strachey, R.E., 

 C.S.I. ; General James Thomas Walker, C.B. 



Surgeon-Major James Edward Tierney Aitchison (elected 1883) 

 was admitted into the Society. 



The Presents received were laid on the table and thanks ordered 

 for them. 



The following Papers were read : — 



I. Ci On the Fertilised Ovum and Formation of the Layers of 

 the South African Peripatus." By Adam Sedgwick, M.A., 

 Fellow of Trinity College, Cambridge. Communicated by 

 Professor M. Foster, Sec. U.S. "Received October 18, 

 1885. 



The Fertilised Ovum and its Nucleus. 



The fertilised ovum of Peripatus capensis contains a central cavity 

 traversed by a few strands of protoplasm. 



The protoplasm has a reticular or spongy structure, the reticulum 

 being very close round the nucleus and much looser elsewhere. The 

 strands of the reticulum are composed of an apparently perfectly 

 homogeneous protoplasm. The nucleus is placed on one side of the 

 ovum ; it is a large body which varies very considerably in shape and 

 structure in different ova. These variations no doubt represent 

 different phases in the life-history of the nucleus. It has been 

 impossible for me with the small number (ten) of unsegmented ova 

 at my disposal to determine their sequence. 



The nucleus of the fertilised ovum is, however, so large and 

 favourable for study that I have thought it worth while to describe 

 three different stages in which I have seen it. 



1. A spherical structure (diameter, 0*04 mm.) bounded by a mem- 

 brane, which is slightly indented at one point, where it sends in a 

 prolongation of itself, which passes through the nucleus to become 

 continuous with the membrane of the opposite side. The nucleus is 

 made up of a fine spongew r ork of very pale fibrils, which are continuous 

 with the nuclear membrane and with the septum just mentioned. In this 

 spongework are a number of deeply-staining more or less spherical 

 bodies. The nuclear membrane and septum appear precisely similar in 

 structure to the strands of the external protoplasmic reticulum, and 

 the latter are continued directly into the former. The pale nuclear 

 reticulum is also similar to the extra-nuclear reticulum, differing only 



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