REPORT ON THE DEEP-SEA KERATOSA. 17 



this legion into two orders, Cannoccela (the Ammoconidse) and Domatoccela (all the 

 other Keratosa). 



The Cannocoela, represented by the Ammoconidse (PL VIII.), retain either the 

 primordial Ascon-type, the Olynthus-f orm (Ammolynthus, figs. 1, 2), or they form branched 

 tubular bodies, composed of a few or numerous Olynthus-tuhules ; the branches are 

 either free, each possessing a terminal osculum (Ammosolenia, fig. 3), or are connected 

 by anastomoses, and form a reticular framework (Ammoconia, figs. 4, 5) ; the wall 

 of the delicate tubules is in all these Ammoconidse very thin, supported by a delicate 

 mesoderm-lamella (as in the Asconidse), and is pierced by small simple pores ; the 

 sea-water entering by these pores is propelled by the flagellated collar-epithelium, 

 which lines the whole inside of the tubules, and issues finally either by the distal 

 oscula or by other pores. Each branch of the Ammoconidse, as well as of the similar 

 Asconidse, is to be regarded as a secondary Olynthus, and at the same time homologous 

 to a single flagellated chamber in the second order, the Domatoccela. 



The Domatoccela (corresponding to the Heteroccela in the Calcarea) are represented 

 among the Deep-sea Keratosa by three families, the Psamminidse (PL VII.), the Spon- 

 gelidsa (Pis. IV- VI.), and the Stannomidge (Pis. I.— III.). All the horny sponges hitherto 

 described belong to the Domatoccela. The main mass of their body is formed by a 

 voluminous mesoderm, or a kind of connective tissue, and this is permeated by a 

 complex canal-system. The outer surface of the mesoderm is covered by a delicate 

 pavement-epithelium and pierced by innumerable microscopical pores ; the water enters 

 through these pores into ramified canals, and is propelled by the vibratile motion of 

 flagellated entoderm-cells, which line the characteristic " flagellated chambers " disposed 

 in a variable manner along the canals ; from these the water issues by canals, which 

 open finally by smaller or larger exhalent openings (oscula). The special structure of 

 this domatoccelous canal-system (as far as it could be recognised in the three families 

 examined) is essentially the same as in the Spongelidae, with large sac-shaped flagellated 

 chambers (Macrocamerje, Lendenfeld). 



Skeleton. 



The varied and manifold development of the skeleton, which is the main principle in 



the classification of the numerous genera and species of sponges, is also in the Deep-sea 



Keratosa of the greatest importance. It offers, too, here certain remarkable features 



which are not fouDcl in the Keratosa hitherto known, and some peculiarities which are 



cpiite new. The causes of this peculiar development may be searched for partly in 



the peculiar conditions of deep-sea life and the adaptation of the organism to the abyssal 



bottom, partly in the curious symbiosis, to which the majority of the Deep-sea Keratosa 



are subject. 



(zool. chall. exp. — PAET lxxxii. — 1889.) Nnnn 3 



