284 LILIAN SHELDON. 



strands connecting the two being clearly visible. I have 

 found the male pronucleus in this condition in three ova of 

 P. capensis. 



I have seen no ova of P. capensis in which the union of 

 the pronuclei is taking place, though I shall shortly describe 

 one of P. Balfouri, in which the male and female pronuclei 

 lie close together in the centre of the ovum, and are apparently 

 about to conjugate. In the next stage of P. capensis the 

 union has apparently taken place, and the nucleus is a large 

 lobed structure lying some little way from the periphery. It 

 is not surrounded by a large and definite mass of denser pro- 

 toplasm, but only by a very narrow layer, which almost imme- 

 diately passes off into the loose reticulum which fills up the 

 rest of the ovum. 



In the next stage the segmentation nucleus is fully formed ; 

 it lies near the periphery, and is surrounded by a specially dense 

 mass of protoplasm, which, as Mr. Sedgwick (14) has stated, 

 causes the dark patch which is seen on these ova, by means of 

 which, even after preservation, the prse-segmentation ova can 

 be readily distinguished from those in which the segmentation 

 nucleus is present. I have not figured ova of this stage, as 

 Mr. Sedgwick (14) has already done so (PI. Ill, figs. 8 

 and 11). 



Pebipatus Balfouri. 



The phenomena connected with the maturation and fertili- 

 zation of the ovum in P. Balfouri are very much the same 

 as in P. capensis, and therefore I shall merely describe the 

 differences between the two, and one or two stages which I 

 have found in the former, which were wanting in the latter. 



Structure of the Ovary. — A section through one half 

 of the ovary is shown in fig. 22 ; its structure in the main is 

 the same as that of P. capensis, but the germinal area is 

 much narrower, being confined to a narrow strip along the 

 outer side of each ovarian tube. The non-germinal epithelium 

 is also very much thinner ; and, in fact, has the appearance of 

 a membrane with small bulgings on it caused by the nuclei. 



