3270 WILSON. [Vor. Ix 
«The (once) ciliated cells surrounding the irregular spaces 
arrange themselves so as to form a nearly continuous wall, in 
which, here and there, an intermediary cell is found. This is, 
however, not the permanent epithelium, for intermediary cells 
lying outside it gradually take the place of the ciliated cells, 
which in their turn come to lie outside the definitive epithelial 
wall. Such ciliated cells, which have temporarily been occu- 
pied in lining the canals, now follow the example of their 
brethren and unite to form flagellated chambers.” 
Observations such as are embodied in my Pl. XVIII, Fig. 47, 
and Pl. XVII, Figs. 39 and 42, seem to me to contradict the 
above account. The canals shown in these figures are evi- 
dently just forming, and yet their walls are made up of 
elements which, to judge from Delage’s figures, I must con- 
clude he would regard as amoeboid and intermediary, certainly 
not as immigrated ciliated cells. 
Finally, the distinction which Delage makes between inter- 
mediary and amoeboid cells, is to my own mind an artificial 
one. His amoeboid cells evidently correspond to my forma- 
tive cells, but I find no special place for his ‘‘ intermediary ” 
group, because the plump formative cells are being constantly 
changed into elements which Delage would class as interme- 
diary. An instance of this is found in the development of the 
dermal membrane, where formative cells are gradually trans- 
formed into the slender elongated cells forming the mesoderm 
of this membrane (az?e, p. 307). 
Note. — While this paper is passing through the press, a new contribu- 
tion to the subject by Otto Maas appears.!' The author has studied a large 
number of marine cornacuspongiae and has worked over the development 
of Spongilla. His account of the metamorphosis for all these forms differs 
but little from his previous account of the metamorphosis of the Esperia 
larva. In some points Maas differs from Delage’s recent conclusions. 
Thus Maas does not find that the ciliated cells of the larva are engulfed by 
the amoeboids and subsequently liberated. No such peculiar association 
of the two kinds of cells occurs. With this I thoroughly agree, although 
differing entirely with Maas in the general view of the metamorphosis. 
Again Maas states that in those larvae with a “bare” posterior pole, like 
1 Die Embryonal-Entwicklung und Metamorphose der Cornacuspongien. Zoolog. 
Jahrbiicher, Abth. fiir Anat. und Ontogenie. Bd. VIL, 2. H. 
