REPORT ON THE MONAXONIDA. 



257 



Tablk of Geographical and Bathymetrical Range — continued. 



DISCUSSION OF THE GEOGRAPHICAL DISTRIBUTION. 



In glancing over the list of localities at which Monaxouid sponges were obtained, one 

 can scarcely fail to be struck with their small number as compared with the total number 

 of dredgings made by the Challenger. Out of a total of 277 distinct stations we 

 find only 50 represented in the collection, supplemented by 20 "localities" to which 

 no station number is attached. 



This is a very remarkable circumstance ; it is probably to be accounted for partly by 

 the fact already pointed out in our Introduction (p. v), viz., that the Monaxonida 

 are, as a rule, very insignificant and uninteresting in external appearance, and hence 

 extremely likely to be overlooked amongst the rubbish in sorting out the contents of the 

 trawls and dredges, unless a specialist be on the spot to look out for them, and also 

 partly by the fact that the sponges in question are usually very soft and fragile, and 

 hence peculiarly liable to destruction by the rough treatment to which they are necessarily 

 exposed in trawling, and, more especially, dredging operations. 



These explanations are, however, hardly sufiicient to account entirely for the absence 

 of Monaxonida from the great majority of localities examined by the Challenger, and we 

 are forced to conclude that the Monaxonida are not, on the whole, a predominant group 

 in deep water, although, as we shall subsequently show, individual genera range down to 

 very great depths, and are occasionally, but very rarely, found in great abundance in 

 deep water {e.g., Station 320). Thus, as the Challenger confined its operations mainly to 

 deep water, we have an explanation of the facts before us ; an explanation precisely 

 similar in kind, though not so far reaching in degree, as that arrived at by PolejaefF in 

 the analogous case of the Keratosa. 



Conversely, we find that in those cases where explorations were made by the 

 Challenger in shallow or comparatively shallow water, rich harvests of Monaxonid 



(ZOOL. CHALL. EXP. — PAHT LIX. — 1887.) Nnn 33 



