Hyatt.] 86 [March 5, 



giae appear, however, to decide that this term cannot be admit- 

 ted. The lining cells of the gastro -vascular cavity are not at 

 first ciliated and the ampullae, according to Marshall, arise in con- 

 nection with them by invagination of the lining cells of the main 

 cavity. The cells which line the lateral cavities or ampullae do 

 not, however, retain the characteristics of the epithelium from 

 which they originated. They acquire collars or funnels on their 

 free ends and also fiagella. 



We think it will be found convenient to apply the term 

 Ascula to the first period of attachment, that in which the 

 sponge has lost or is just losing the collar, opening the primitive 

 cloacal crater, and forming the first central cavity without lateral 

 ampullae. We have not been able to separate the Protospon- 

 gian stage of Haeckel from the ascula and think it should be 

 merged in the latter. The cinctoplanula cannot be considered 

 to be identical with this or the ascula, or to imply an ancestral 

 form such as the protascus of Haeckel. It indicates the pre- 

 vious existence of a stock of forms more differentiated than the 

 parenchymula and quite distinct from the hydroplanula, but 

 certainly not a protascus. We can conveniently use Haeckel's 

 name of Archispongia for these supposed ancestors, and, there- 

 fore, employ it in this sense. 



According to our experience among fossils, especially Cepha- 

 alopoda, there is no stable characteristic of the young, however 

 minute, without its forerunner in the adult of some ancestor; 

 and we think, therefore, that the collar, though apparently 

 an egg-organ, indicates an adult ancestral type possessing a 

 similar structure. We realize that there may be important 

 organs which appear in the larva, and have never been possessed 

 by adults, but many are hastily assumed to be of this kind before 

 being proved to be so. Even the egg-tooth of birds and rep- 

 tiles, though possibly one of this class, depends upon negative 

 evidence, and may at any time be shown to have a genetic sig- 

 nificance. While believing in mechanical evolution and purely 

 physical forces, it seems not at all philosophical to accept even 

 apparently obvious reasons without close examination. Adapta- 

 tion has been assumed with reckless prodigality as sufficiently 

 accounting for the origin of characteristics and forms in the lar- 

 vae, especially of insects, when experience teaches that similar 



