N'lTKoLLrLA FEKTILItf. ÖO 



together into a 1>iuich, llieiice to project tlieir pointed emlri for a 

 short distance out of the soft tissue. 



Finally, some remarks on the develo])menl. 



In all appearance the larva originates from the arclueocyte- 

 congeries of the mother individual. In this respect T have 

 nothing to add to what I have said in Contrib. I., ])p. 18 7-11 X), 

 and in Contrib. ill., pp. 42, 43.=^= PI. III., figs. 13-15, will give 

 a fairly good idea of how arclueocyte-congeries of various sizes 

 appear in sections. In them the external epithelial layer of the 

 larvffi is still undeveloped. This comes into formation when a 

 congeries has attained a diameter of 90-100 //, by which time it 

 is invariably spherical in form. I must say that there can not 

 be discovered in my series any stages which show the exact 

 manner of the formation of the external epithelium. Xeverthe- 

 less, I think it will not fall wide of the mark to assume that 

 the peripheralmost cells in a congeries, which has grown to the 

 proper size, take the epithelial arrangement and thus difterentiate 

 themselves as a layer from the inner cellular mass. Possiljly 

 this takes place synchronously with the development of flagella 

 by the said cells. At any rate, the remnants of flagella in the 

 foi'm of a clear, granidai' or striated-like crust are observable as 

 soon as the external e})itheliuni has established itself as such. 

 Whether the epithelium is at first formed alike all over the 

 spherical embryo, must be left undecided. The ap})earance of 



* 111 Sonic 111' the sectiuns of VilroUnhi ferllll" I liavf mot with a few cases of veritahle 

 ej;ss whicli were undergoing llie cleavage process. They measured ahout TOO \i. and were of 

 a dark appearance owing to llie abundant presence of deuto[)hismic granules wliicli com- 

 pletelv hid the nuclei. However, I liave made myself sure of tlie fact that they did not 

 lielong t(j the sponge, hut to a small Crustacea which lived in the sponge-wall, — a fact 

 which could at once be foretold from the very appearance of the vitellus. 



