438 M. Karl Fiedler on the Development of the 



correspond to the cells described by Polejaeff* in his ' Chal- 

 lenger ' Calcarea, to which he ascribes " nutritive functions," 

 and, indeed, in tlie sense of " reception of nourishment." In 

 Spongilla they were first observed by Weltner (of Berlin) 

 and subsequently, but independently, by myself. They are 

 also diffused through the whole sponge-body, but are parti- 

 cularly abundant beneath and even between the cells of the 

 cuticle, and here again often in the vicinity of the inhalant 

 apertures. Their regularly granulated plasma then contains 

 further more intensely coloured particles of irregular form. 

 If the latter, as seems most probable, are incepted nutritive 

 constituents, this would be in agreement with the above-cited 

 notion of Poldjaeff, and would also explain von Lendenfeld'sf 

 statements with regard to the inception of nourishment 

 through the external surface of the sponges, without the 

 ectodermal cells needing to take part in the operation. As 

 Weltner proposes to make further communications upon the 

 peculiarities of these cells, I shall confine myself to these indi- 

 cations. Only I may say further that the ovicells are not to 

 be referred to these uniformly granulated cells, but to the 

 wandering cells of the ordinary kind. 



The growing ovum, which, in earlier stages, sometimes 

 shows a remarkable radiation of the plasma, now becomes 

 gradually more and more filled with vitelline granules. The 

 nucleus, however, never entirely disappears. But while at 

 first it always occupies the middle of the ovum, we find it now 

 most frequently removed close to the surface. In both cases 

 it is surrounded by a circle of plasma comparatively poor in 

 vitelline material. There can be no doubt that this remark- 

 able change of position in the nucleus is connected with the 

 elimination of the so-called direction-corpuscles. In fact I 

 repeatedly observed in the neighbourhood of the nucleus two 

 considerably smaller but no less vividly coloured chromatin- 

 particles, which are probably to be characterized as the abcon- 

 stricted direction-corpuscles. Thus this important process, 

 recently interpreted with so much genius by VVeismann J, is 

 rendered probable even for the lowest group of the Metazoa. 

 Unfortunately I did not succeed in tracing, on the one hand 

 the formation of the direction spindles, or on the other tlie 

 process of fertilization. It is clear, however, that the nucleus 



* N. Polejaeff, "Report on the Calcarea dredged by H. M.S. 'Chal- 

 lenger,' " in Report, vol. viii. p. 6 (1883). 



t R. von Lendenfeld, "Neue Ccelenteraten derSiidsee, II. NeueAplv- 

 sinidae," in Zeitschr. fiir wiss. Zool. Bd. xxxvii. p. 2-34 (188.3). 



X A. Weisnmnn, " Ueber die Zahl der Richtimgskorper und liber ihre 

 Bedeutung fur die Vererbung," Jena, 1887. 



