GENERAL REMARKS ON THE ORGANISATION OF THE 



DEEP-SEA KERATOSA. 



The general organisation of the sponges is widely discussed in the voluminous and 

 most valuable reports on the various main groups of this class, which form such an 

 important part of the Challenger work, viz. : — Sollas on the Tetractinellida (Zool. Chall. 

 Exp., part lxiii. vol. xxv., 1888), F. E. Schulze on the Hexactinellida (Zool. Chall. Exp., 

 part liii. vol. xxi., 1887), Ridley and Dencly on the Monaxonida (Zool. Chall. Exp., part 

 lix. vol. xx., 1887), Polejaeff on the Keratosa (Zool. Chall. Exp., part xxxi. vol. xi., 1884), 

 and Polejaeff on the Calcarea (Zool. Chall. Exp., part xxiv. vol. viii., 1883). The greatest 

 part of the general morphological and physiological considerations which are given in 

 this rich series of reports, and mainly in those of Sollas and F. E. Schulze, may be 

 accepted also for the small group of sponges which are described here as Deep-sea 

 Keratosa. To avoid repetitions, therefore, it is sufficient to refer to the last-named 

 reports, and to add here only a few short remarks on those peculiarities which deserve 

 special attention in the organisation of the horny sponges of the deep sea. 



Individuality and External Form. 



The external form of sponges, as is well known, is extremely variable, and is generally 

 of little morphological importance, since often sponges of very different internal 

 structure possess the same external form, and, on the other hand, often two closely allied 

 sponges are quite different in external shape. This is easily explained if we consider as 

 the simplest individual sponge the Olynthus, or a Gastrsea-like simplest tubular person, 

 and if we assume that the body of most sponges is a corm or stock composed of 

 numerous such persons, viz., the flagellated chambers (or, in the Asconidse and 

 Ammoconidse the equivalent branches of the tubular body). The external form of the 

 corms or stocks (in contradiction to that of the component persons) is very variable, and 

 subject to adaptation also in other classes of corm-building lower animals, e.g., in the 

 closely-allied Hydroids and Corals (Hydrozoa and Anthozoa). When we compare the 

 single individuals (persons or zooids) of a massive corm of Hydroids or Corals and the 



