442 Gr. C J. Vosmaer 



cells, lately described by Polejaeff ^ were visible, althougli I am well 

 acquaiüted with their appearance. 



I meütioned the fact that I could not see spongoblasts. This is how- 

 ever no reason at all that the skeleton of Velmea shoiild develop in 

 another way. One must not forget that only one specimen, preserved 

 in spirit, was at my disposai. — The fibres consist of a pith - substance 

 (Marksubstanz) and concentric layers of Spongin around it. This pith- 

 substauce has not always the same diameter, but there is always a trace 

 of it. Sometimes the outer spongin-layer has stained clearly while the 

 pith has remained yellowish. In that case the difiference is very well 

 Seen on transverse sections ; but often the colour diminishes gradually 

 towards the eentre. In fig. 1 1 the pith is visible, although not at first 

 sight; in fig. 12 it is very conspicuous. The cells in the fibres, as von 

 Lendenfeld has described in some Aplysitiidae, seem not to occur. The 

 fibres resemble much more those ai Spongelia than <òi Aplysina ax Äply- 

 silla. The curious yellow highly refractive corpuscles, described by Oscar 

 Schmidt and F. E. Schulze in Euspongia were abundant in Velmea 

 (fig. 11 and 12). It is remarkable that they occur sometimes in the 

 pith (fig. 12) at other times between the spongin - layers (fig. 11). 

 I do not know what these corpuscles are. No trace of plasma or 

 nucleus was to be seen. I showed my preparations to Dr. Karl Brandt 

 and asked him whether he had ever seen «yellow cells« resembling these 

 corpuscles. Ile answered that they had nothing to do with them. In 

 fig. 13 I bave made a picture of a fibre that has been boiled inEau de 

 Javelle. There are no yellow corpuscles to be seen ; this is perhaps 

 because they are not present since they can resist for a long time the 

 action of reagents. 



As regards the systematic position of Velmea, I believe ìt 

 to be nearly allied to Spongelia. 



It will be necessary to consider the whole group of those Sponges 

 which exceptiug the horny skeleton do not produce any other substance 

 for strengthening it, viz. of the so-called Hornsponges. 



For the moment there are to be distinguished four groups of Horn- 

 sponges. Io the first place we bave the family of the Aplysinidae, cha- 

 racterised by the fact that the fibres of the skeleton possess nearly al- 

 ways a thick axis-substance and are without foreign corpuscles; in 



1 Polejaeff, Sitzungsber. Ak. Wiss. Wien. Bd. LXXXVI, p. 276-29S. 

 I bave seen these cells in many other sponges. I showed my sections to Dr. Pole- 

 jaeff, who was kind enough to study them ; he told me that I had been right in 

 identifying the cells in qnestioa. 



