626 REVIEW. 



unknown in the bay and hitherto undescribed. It outwardly 

 resembles S. capillosa. Vosmaer's views on Leucandra 

 aspera {' Mitt. Zool. Stat. Neapel./ vols, iii and iv) may require 

 some modificationj but its variation is certainly enormous. It 

 is true that the Homocoela of Naples seem fairly constant in 

 outward form and canal-system (sensu Dendy), but evidence 

 points to their being identical with species of very different 

 aspect in other localities. I disagree with Mr. Dendy that 

 " there is no doubt that a species has no existence in nature.'^ 

 This, however, is an academic question of general zoology, 

 which should be treated by more competent hands than mine. 

 In his rejection of von Lendenfeld's Homodermidse and 

 Leucopsidse he has taken the only course open. It is to 

 general advantage that it should be stated plainly that the 

 histology figured in Homoderma is alone sufficient to con- 

 vince any student of C ale are a that the structures described 

 were never seen. 



The attempt to group the Homoccela according to structure 

 is valuable and suggestive. It does not claim to be sufficiently 

 developed to be considered as a natural classification. There 

 are three sections of the Homocoela : I. Simplici a, solitary, or 

 with individuals of easily recognised individuality. II. Reti- 

 cula, anastomosing tubes, in which individuals are unrecog- 

 nisable. III. Radiata (one species), a (large) central 

 Ascon-tube bearing secondary radial tubes. The last group 

 or species (Leucosolenia tripodifera) is perhaps the most 

 important discovery recorded in the paper. The radial tubes 

 branch and branch again, until they are set thickly together 

 like a wall round the wide central osculate sac into which they 

 open, so as to simulate precisely the canal-system of a Sycon. 

 But the central tube retains its collar-cells and pores, and 

 its true wall differs in no structural respect from that of its 

 tributaries. 



This observation and its treatment by the author appear to 

 me most suggestive. I think that an examination of inter- 

 mediate forms will convince him that there are many other 

 Homocoela to be included in the Radiata. Ascandra 



