332 WILSON. [Vol. IX. 



points, the larvae of Tedania and Esperella are essentially 

 identical.) Next after the mass of pale cells comes an aggre- 

 gation of large granular well-staining cells, gr. c, Figs. 78, 81. 

 Following upon the granular cells, the axial part of the larva, 

 ax. p.. Fig. 81, is occupied by a mass of slenderer and less 

 granular cells, provided with delicate processes, many of the 

 cells being bipolar. This part of the larva is considerably 

 denser than the peripheral part, /^r. /., in which the cells are 

 relatively less numerous, many of them lying in a more or less 

 radial direction, parallel with the short spicules, which in the 

 swimming larva are confined to this region. Besides the cells 

 mentioned, there are found scattered here and there through 

 the body of the larva a small number of very coarsely granular, 

 deeply staining cells. A few of them are shown in Fig. 78, 

 lying amidst the pale cells at the end of the larva ; others are 

 shown in Fig. 81, some of them in the ectoderm, others in the 

 axial part of the larva. As in the case of Esperella, so in this 

 larva, there is a loose bundle of long spicules in the unpig- 

 mented end of the body, Figs. 78 and 81. The spicules are the 

 tylotes with nicked heads. The strongyloxeas, the spicules 

 which in the adult form the skeletal meshwork, do not appear 

 in the swimming larva. 



There is only one noticeable change which occurs in the 

 larva during its short swimming life, and which concerns the 

 unpigmented pole. When the larva is just born, this pole does 

 not protrude to any great extent. Fig. •]%. Indeed, quite often 

 this end of the body is pulled in, Fig. 79 (surface view of larva 

 just escaped from parent sponge). But after fifteen or twenty 

 hours of larval life, it is found that the unpigmented end 

 protrudes to such an extent, that it is a very conspicuous 

 feature of the living larva. Fig. So. (Surface view of a lar\'a a 

 day old. In this figure the peripheral zone of short spicules is 

 shown.) In sections, too, this difference between larvae just 

 born and older ones, is noticeable — compare Figs. 'jZ and 81. 



3. Metamorphosis. 



Attachment. — With most individuals the swimming life lasts 

 about a day, with some two and three days. Towards the end 



