232 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, gv.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, per. f., 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. 78. 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. 80. (Surface view of a larva 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. 78 and 81. 
3. METAMORPHOSIS. 
Attachment.—With most individuals the swimming life lasts 
about a day, with some two and three days. Towards the end 
