iS95. RESULTS OF ''CHALLENGER" EXPEDITION. 35 



The Calcarea and the Keratosa were reported on by N. Polejaeff ; 

 the Monaxonida by S. O. Ridley and A. Dendy ; the HexactinelHda 

 by F. E. Schulze ; the Tetractinellida by W. J. Sollas ; and the Deep- 

 sea Keratosa by Ernst Haeckel. In all 1,736 pages of letterpress, and 

 226 plates were required for the elucidation of this interesting group. 



It is a subject for congratulation that the eminent naturalist, 

 Professor Haeckel, whose work on the Radiolaria would alone have 

 proved exhaustive to most mortals, was able to spare some of his 

 attention for the study of a class, with which his name must ever be 

 indissolubly connected. The inspiration of the " Kalkschwamme" was 

 still an influence genially working in the minds of all the colleagues 

 associated with him in the study of the " Challenger " sponges. 



We are indebted to Professor Haeckel for the following account 

 of his work on " The Deep-sea Keratosa " : — 



The twenty-six species which are comprised in this group, and 

 which are all new, belong to eleven different genera and four 

 families. These sponges are very remarkable by reason of their 

 peculiar pseudo-skeleton and their symbiosis with hydroid polyps. 

 The main mass of the body is composed either of siliceous Radiolaria 

 shells or of calcareous Foraminifera shells. The place of an internal 

 skeleton made by the animal itself is taken by the reticular hydrorhiza 

 of the hydroids living in symbiosis with the sponges. Some of the 

 larger species have the form of a broad flabelliform leaf, and their 

 transverse diameter reaches 20 cm. or more [Stannophylhiin) ; some 

 other smaller forms {Ammolynthus) are simple urn-shaped utriculi, not 

 longer than 6-12 mm., and i-i"5 mm. broad; they are among the 

 simplest and most primitive sponges that we know. The whole 

 structure of these Deep-sea Keratosa is so peculiar that many 

 experienced naturalists who had previously examined them expressed 

 the most different opinions as to their true nature. It required a very 

 careful study before I could confirm the view of Dr. John Murray 

 (stated immediately after their capture) that they were undoubtedly 

 true sponges. 



Ernst Haeckel. 



When Polejaeff commenced the study of the Calcarea, some 

 ten years had elapsed since the publication of the " Kalkschwamme " 

 by Haeckel, and in this interval great improvements had been intro- 

 duced into the methods of section-cutting, so that a means was 

 provided by which Polejaeff was enabled to undertake a critical 

 revision of the calcareous sponges, a task which, in spite of the 

 comparatively small amount of material at his disposal, he accom- 

 plished with the most transparent success. A re-modelling of the 

 classification of the group was one result, an exact knowledge of its 

 anatomy and histology another. 



The transition which Polejaeff was able to demonstrate as 



occurring between the Sycon and Rhagon type of chamber-systems 



within the limits of the Calcarea is a fact of great interest, and the 



knowledge which we now possess of the chamber-system in this and 



other groups of sponges affords evidence of a strict homoplasy 



between the successive stages of development of this system in the 



D 2 



