39 Miss J. E. Lane-Claypon. On the Origin, 'etc., of [June 16, 



Origin of Interstitial Cells. By about the tenth day the ovogenetie 

 processes in the central egg-clusters are at their height, and continue in 

 this condition, passing through the various phases, until about the fourteenth 

 day, when, as_already stated, some have reached their final stage. Through- 

 out the whole period, however, there are in almost all the clusters some three 

 or four cells, or perhaps more, which remain in the ordinary deutobroque 

 state, and do not undergo any of the ovogenetie phases, the number of these 

 being greater in the peripheral clusters than in the central ones ; by the 

 fifteenth and sixteenth days, when the number of dictyate nuclei is increasing, 

 there are few, if any, of the deutobroque cells to be found in the central parts, 

 but instead, there is an increasing number of the small round cells already 

 referred to. As the days pass on the number of the former decreases, 

 and the number of smaller cells increases. Thus, there is throughout the 

 ovary, but in different parts at slightly different periods, a reduction in the 

 number of deutobroque cells, which have remained unchanged, and an 

 increase in the number of small round cells. 



Examination of sections of the fourteenth, fifteenth, and sixteenth days 

 near the centre of the ovary, leaves no room for doubt that some of these 

 cells form the follicular epithelium, gradually passing towards and arranging 

 themselves around the young ova. At the fourteenth day the number of 

 these cells to be found near the centre is not nearly sufficient to form the 

 follicular epithelium for the large number of young ova, while near the 

 periphery there are many more than would appear to be necessary for the 

 requirements of this part. By the fifteenth day the number of these cells 

 near the centre has increased very largely, still more so by the sixteenth day, 

 by which time many of the young ova are surrounded with follicle cells, and 

 there are also the collections of these cells already referred to. Their number 

 has meanwhile diminished somewhat at the periphery. The appearance in the 

 intermediate parts gives the key to the whole question. Here are seen la-rge 

 numbers of these cells streaming inwards from the periphery and making 

 their way between the egg-clusters of the periphery towards the centre, 

 where the cluster formation can now be scarcely recognised. Here they 

 arrange themselves around the young ova, or pass into little groups by 

 themselves. These groups are the first beginnings of the real interstitial 

 tissue of the ovary, and mark the commencement of the adult aspect of the 

 organ. 



There are thus two main points to be emphasised at this period in the life 

 of the ovary. First, the passage inwards of a large number of cells from the 

 periphery, and secondly, the commencement of the adult formation by the 

 formation of young follicles, and the appearance of interstitial cells. 



