34 THE VOYAGE OF H.M.S. CHALLENGER. 



Hircinia, 1 — be but one alternative possible : either the physiological explanation I have 

 given 2 of the existence in the spermospores of a covering cell is really right, or, if the 

 covering cell is of a more profound morphological signification, it ought to be present in 

 the spermospores of all the Sponges. This last supposition is, of course, very plausible ; 

 I must add, however, that hitherto my search for this structure in Aplysilla and Halisarca 

 has proved unsuccessful. 



1 Ibid., vol. xxxiii. p. 28, 1880. s hoc. rit., p. 292. 



