Sexual Products in Bpongilla. 437 



ance at first, but tliat tliej are preceded bj all possible stages 

 of smaller vitelline elements. A regular arrangement, such 

 as that the vitelline globules increase in size from the peri- 

 phery to the centre, is not, however, to be observed. 



The follicle-cells I regard siraplj as parenchyma-cells 

 pressed against each other by the pressure of the growins; 

 ovum, and so flattened against each other. Some of them I 

 would characterize as specific nutritive cells, taking this notion 

 more in the sense adopted by F. E. Schulze, Keller, &c., 

 than by Goette. Thus in preparation with Flemming's 

 chrom-osmium-acetic acid mixture, besides the vitelline 

 granules of the ovum, many of the cells surrounding the ovum 

 undergo an intense blackening of their contents. The num- 

 ber of cells of this kind which also occur isolated in the rest 

 of the sponge-body constantly increases up to a certain time 

 exactly in the neighbourhood of the ovicells. Frequently 

 they penetrate with their amoeboid processes between the 

 ordinary follicle-cells and towards the ovum itself, but without 

 uniting with the latter. They do not contain ready-made 

 vitellus, as the above-mentioned blue staining material does 

 not produce in them the same reaction as in the ovum. On 

 the other hand, they prepare in their bodies a material which 

 is to be regarded as a fore-stage of the vitellus, and which is 

 given off to the ovum by the process of diffusion. Fven 

 after the first segmentations we notice a distinct diminution 

 in the number of such blackened cells, and the ordinary 

 follicle-cells also become fainter, if I may so express myself. 

 Finally, the products of segmentation are surrounded only by 

 a very delicate follicular membrane, which certainly has no 

 longer any actively nutritive function. But even if, at first, 

 several cells contribute to the nourishment of the ovum, the 

 latter, as Korschelt* aptly remarks in a similar case, "does 

 not, by the inception of secretion-products of other cells^ lose 

 its own cell-nature any more than an Amoeba loses its uni- 

 cellularity by the inception of food. The characteristic is the 

 living capacity of assimilation of both towards the nutritive 

 material offered to them." 



We have to distinguish from the nutritive cells above 

 described certain amoeboid wandering cells of another kind, 

 the bodies of which are filled, not with irregular granulations, 

 but quite uniformly with particles of considerable size ; only 

 occasionally a perfectly hyaline marginal zone occurs. These 



* E. Korschelt, " Ueber die Entstehung und Bedeutung der verschied- 

 enen Zellenelemente des Insectenovariiims," in Zeitschr. fiir wiss, Zool. 

 Bd. xliii. p. 6y0 (1886). 



