545 



lüsette-like. I have never succeeded in observing ova in the act of 

 being discharged, but there can be no doubt that they pass out in the 

 same manner as the spermatozoa — their passage through the rather 

 narrow canal being favoured by their extreme viscosity. In specimens 

 of Polynoe perclara with ripe sexual products the parapodia are beset 

 at their bases with rows of long cilia so arranged as to drive anything 

 discharged from the segmental organs upwards towards the cavity be- 

 neath the scales, where, as is well known, the eggs undergo the earlier 

 stages of their development. This arrangement would have no mean- 

 ing were it not intended for the transportation of the eggs from their 

 points of discharge at the ventral surface to their brood-pouch beneath 

 the elytra. In Lepidonotus oculatus this special arrangement of cilia is 

 absent ; and it is to be remarked that in this species, of which I have 

 examined many specimens with ripe sexual products, the eggs do not 

 seem to be hatched beneath the elytra, which are small, not covering 

 the whole back. 



Apertures have been described in the walls of the parapodia and 

 through these it has been supposed that the ripe ova and spermatozoa 

 are discharged. I have never found any such apertures in the species 

 examined by me; rows and circlets of cilia frequently occur; these are 

 set in rectilinear or circular slits in the cuticle, the cilia being prolon- 

 gations of the subcuticular layer, and this arrangement may in the case 

 of the circlets give rise to the appearance of circular apertures. It must 

 be added, however, that those species in. which I have made certain 

 that no such apertures exist were examined only during -the breeding- 

 season. It may be that apertures, open at other seasons, are closed at 

 that time to prevent the sexual elements from escaping through any but 

 the proper channels. Be this as it may, it does not affect the main 

 question with which this paper is concerned — viz. the position and 

 relations of the true segmental organs. 



2. Variation in the Yolk-cleavage of Renilla. 



By Edmund B. Wilson, assisted by H. L. Osborn and J. Meredith Wilson. 

 (Note from the Marine Laboratory of the Johns Hopkins University.) 



During the months of May and June the ripe eggs of licnilla re- 

 niformis Cuv., were obtained in abundance at Beaufort, N. C. and I have 

 been able to make a full study of the phenomena of segmentation. 

 When studying a number of eggs it was found that the segmentation 

 was not of a uniform character but presented a surprising and unpre- 

 cedented amount of variation. 



This observation appeared of such importance as to render desi- 



