SPONGES 86 I 



tloltenia Car j)e uteri, of which four specimens, dredged \\p Iroin a 

 depth of 5:>0 fathoms between the Faroe Islands and the north of 

 Scotland, were among the most valuable of the 'treasures of the 

 deep ' obtained during the first deep-sea exploration (1868) carried 

 out by Sir Wyville Thomson and the Author. This is a turnip-shaped 

 body, with a cavity in its interior, the circular mouth of which is 

 surrounded with a fringe of elongated silicious spicules : whilst from 

 its base there hangs a sort of beard of silicious threads that extend 

 themselves, sometimes to a length of several feet, into the Atlantic 

 mud on which these bodies are found. The framework is much 

 more massive than that of Eujdn'tdln. but it is not so exclusively 

 mineral ; for if it be boiled in nitric acid it is resolved into separate 

 spicules, these being not soldered together by silicious continuity, 

 but held together by animal matter. Besides the regular sex- 

 radiate spicules, there is a remarkable variety of other forms, which 

 have been fully described and figured by Sir Wyville Thomson. 1 

 One of the greatest features of interest in this Holtenia is its 

 singular resemblance to the Ventricufotes of the Cretaceous formation. 

 Subsequent investigations have shown that it is very widely diffused, 

 and that it is only one of several deep-sea forms, including .some 

 of singularly beautiful structure, which are the existing repre- 

 sentatives of the old ventriculite type. One of these was previously 

 known from being occasionally cast up on the shore of Barbadoes 

 after a storm. This Dictyocalyx puvniceus has the shape of a mush- 

 room, the diameter of its disc sometimes ranging to a foot. A small 

 portion of its reticulated skeleton is a singularly beautiful object 

 when viewed with incident light under a low magnifying power. 



With the exception of the genus S pong ilia and its allies, all 

 known sponges are marine, but they differ very much in habit of 

 growth. For whilst some can only be obtained by dredging at con- 

 siderable depths, others live near the surface, whilst others attach 

 themselves to the surfaces of rocks, shells, lire, between the tide- 

 marks. The various species of (irantia in which, of all the marine 

 sponges, the flagellate cells can most readily be observed, belong to 

 this last category. They have a peculiarly simple structure, each 

 being a sort of bag whose wall is so thin that no system of canals is 

 required, the water absorbed by the outer surface passing directly 

 towards the inner, and being expelled by the mouth of the bag. The 

 flagella may be plainly distinguished with a ;L-inch objective on some 

 of the cells of the gelatinous substance scraped from the interior of 

 the bag ; or they may be seen /// situ by making \ vry thin trans- 

 verse sections of the substance of the sponge. It is by such sections 

 alone that the internal structure of sponges, and the relation of 

 their spicular and horny skeletons to their fleshy substance, can be 

 demonstrated. They are best made by the imbedding process. In 

 order to obtain the spicules in an isolated condition, the animal 

 matter must be got rid of either by incineration or by chemical 



been investigated by Prof. F. E. Schulze, Trans. l{i>//<il S<>f. <;/' Eilin Imryli, xxix. 

 p. 661. 



: See his elaborate memoir in PJ/il. Truns. 187<l. iinrl his Depths of the Sea, 

 1872 p. 71. 



