718 PROF. A. BENDY AND MR. R. W. H. ROW ON 



nucleus, which is spherical in form, and situated at the base of 

 the cell. Larva a parenchymula. 



" Family 2. Leucosolbniid^. Oscular tubes long, arising as 

 distinct individuals from the stolon-like system of basal tubes ; 

 form of the body erect. Monaxon spicules always present ; tri- 

 radiates, if present, typically bilateral in form, with two paired, 

 and one unpaired angles, and with the crystalline optic axis never 

 vertical, but always inclined, to the facial plane of the rays. 

 Collar-cells with the flagellum arising directly from the pear- 

 shaped nucleus, which is situated at, or near, the apex of the cell. 

 Larva an amphiblastula." 



Without entering into a long discvission as to the theoretical 

 value of these diagnoses, we may point out that in some respects 

 they are in actual practice very difficult of application. Only 

 very few of the numerous described species of homocoel sponges 

 have been examined with reference to the mode of origin of the 

 flagellum in the collared cells, the nature of the larva, or the 

 direction of the cr3rstalline optic axis in relation to the facial 

 plane of the spicule. If it were necessary to investigate these 

 very obscure characters in every case, the classification of the 

 group would indeed make slow progress. 



The more obvious characters which Professor Minchin first 

 made use of for the subdivision of the group, viz., the equiangular 

 or alate character of the triradiates and the position of the nucleus 

 of the collared cell, together with the erect or reticulate form of 

 the colony, lose their value when we extend our investigations 

 beyond the familiar British species. The Australian species, 

 Leucosolenia lucasi, L. stolonifer and Ascute uteoides all have 

 the characteristic non-reticulate, " Leucosolenia " form, and all 

 possess oxea (monaxons) ; L. stolonifer and A . uteoides, however, 

 have collared cells with basally placed nuclei, while in L. lucasi 

 the nuclei are apical, though unfoi'tunately the position of the 

 basal granule is — as is always the case in specimens preserved 

 without very special precaiitions — indeterminable. In L. stolonifer 

 and L. lucasi, again, some at any rate of the triradiates are 

 apparently equiangular and indistinguishable from clathrinid 

 spicules. The test concerning the direction of the optic axis is 

 far too difficult to apply accurately to be of any general value. 



As to the larvse, again, not only are these rarely met with in 

 the HomoeoelidsD, but Professor Minchin himself has shown that 

 there is a transition from the one type of larva (parenchymula) 

 to the other type (amphiblastula). He says] (Lankester's ' Text- 

 Book of Zoology,' part ii. p. 75), " The type of parenchymula 

 larva exemplified by Clathrina reticulum (Fig. 59, 1), afibrds an 

 easy transition to the so-called amphiblastula found in Leuco- 

 soleniidce, and in the great majority of the Heteroccela." 



The genus Clathrina of Gray [1867] was originally based on 

 the reticulate form of the sponge colony, and this is still almost 

 the onl^' chai-acter which could be made use of in practice as a 



