48 JOURNAL OF THE 



site poles is a curious phenomenon, but one aside from the 

 problem. 



I doubt very much, however, if any such radical dis- 

 tinction can be drawn between the larvae of the two groups, 

 for it is. a question whether any sponge larva has a par- 

 ticular pole by which it must attach. Even in Sycandra, 

 Schulze (/. c, p. 270) records that exceptional cases occur, 

 which cannot be regarded as pathological, in which fixa- 

 tion takes place not by the gastrula mouth but on the side. 

 Fixation may also be delayed until the gastrula mouth has 

 closed and spicules have begun to appear, in which case it 

 is not stated by what part the larva attaches. In the solid 

 larvae of silicious sponges the variation is much greater. 

 Such larvae attach in some cases by the posterior pole, in 

 others by the anterior pole, and yet in others on the side. 

 All these variations may occur in larvae of the same species. 

 For instance, Maas records that in Esperia he observed 

 fifteen individuals attach by the posterior pole, seventy in- 

 dividuals by the anterior pole, and five or six on the side. 

 It thus appears that in the larvae of silicious sponges at any 

 rate there is no constant point of attachment. 



University of North Carolina, November 7, 1892. 



