1895. RESULTS OF '^ CHALLENGER'' EXPEDITION. 37 



importance. It is noteworthy that it is not so much the large as the 

 minute spicules which were found to possess most significance in clas- 

 sification, and this is true not alone of the Hexactinellida, for Ridley 

 and Dendy found it to hold good in the case of the Monaxonida, and 

 Sollas in that of the Tetractinellida. 



Schulze did not confine his studies to the material obtained by 

 the " Challenger," but extended them to embrace all known material, 

 so that the report on the Hexactinellida is at the same time a 

 veritable monograph. The number of species obtained by the 

 " Challenger " was ninety, of additional species thirty-six ; of new 

 species sixty-nine were described, of previously known forty-six, they 

 were arranged in fifty genera, of which twenty-two were new. (PL v.) 



Ridley and Dendy in their elaborate report on the Monaxonida 

 describe 213 species of which 158 are new, and arrange them in fifty- 

 four genera, of which five are new. They modify and improve exist- 

 ing classifications, and point out that the deep-sea members of the 

 group are usually distinguished by a greater degree of symmetry than 

 those which inhabit shallower waters. (PI. vi., Fig. i.) 



The Tetractinellida, including the stony sponges (Lithistids) 

 share some of the interest which attaches to the Hexactinellida, 

 with which in the early days of spongology they were sometimes 

 confused. Great use was made of the microtome in their investiga- 

 tion, every species being examined in thin slices : in contrast to the 

 Hexactinellids the characters of the soft parts were found to differ 

 considerably in different groups, and thus to furnish useful aid in 

 classification. The chamber-system was found never to fall to the 

 level of the syconate type, it is always rhagose, and presents two 

 very different degrees of complexity, the simpler or eurypylous, and 

 the more complex or aphodal. It is in the Tetractinellida that the 

 sponges seem to culminate, some of their members attaining a degree 

 of specialisation unknown in other groups. 



In addition to the specimens brought home by the " Challenger," 

 all previously described material was made a subject of study, and 

 the results embodied in the Report. Of species obtained by the 

 "Challenger," there were eighty-seven, of which seventy-three were 

 new ; they were arranged in thirty-eight genera, of which eighteen 

 were new. Of additional species 221 were described, and of additional 

 genera forty-five, of which fifteen were new. 



The important question of distribution was fully considered in 

 all the reports, the facts were tabulated, and in most cases subjected 

 to very elaborate analysis. 



During the preparation of the reports, advantage was taken of 

 the fact that so many observers were simultaneously engaged in the 

 study of sponges, to discuss together a scheme for the simpHfication 

 of the nomenclature of spicular forms. Assistance was afforded by 

 Stewart, von Lendenfeld, and Vosmaer in this work, and a consistent 

 system proposed, which has since found very general adoption. In 



