XXIII. 



CHARACTERISTIC DEEP-SEA TYPES. — SPONGES.^ 



We are led by the study of the Sponges to some of the most 

 interesting biological problems. All our ordinary notions of 

 individuality, of colonies, and of species are completely upset. 

 It seems as if in the sponges we had a mass in which the dif- 

 ferent parts might be considered as organs capable in themselves 

 of a certain amount of independence, yet subject to a general 

 subordination, so that, according to Haeckel and Schmidt, we 

 are dealing neither with individuals nor colonies in the ordinary 

 sense of the words. 



As Schmidt well says : " From the variability of all charac- 

 ters our ideas of an organism as a limited or centralized indi- 

 vidual disappear in the sponges, and in place of an individual 

 or a colony we find an organic mass differentiating into organs, 

 while the body, which feeds itself, and propagates, is neither an 

 individual nor a colony." 



We shall specially dwell on the more prominent Hexactinel- 

 lidse and Lithistidse of the Caribbean district. These groups 

 date back to the lower silurian, and take an extraordinary de- 

 velopment in the Jura ; they are quite abundant in the upper 

 cretaceous, but poorly represented during the tertiaries. Wyville 

 Thomson was perhaps the first to insist upon the relationship of 

 the Hexactinellidse with types of former geological periods, the 

 Ventriculites of the chalk. They, like the Lithistidae, the re- 

 mains of a second fossil family, are in decided minority in the 

 seas of to-day. 



The absence of siliceous and other sponges in the collections 

 made along the northern part of the east coast of the United 

 States is very striking, and although the number of specimens 



^ The account of the sponges has been Oscar Schmidt on the Atlantic and Carib- 

 prepared from the memoirs of Professor bean sponges. 



