214 SCIENCE PROGRESS. 



spongice, the one characteristic of the families Desmacidonidce 

 and Axinellidce, the other of the families Homorhaphidce 

 and Heterorhaphidce (Gellius). In the first type the layer 

 of flagellated cells covering the anterior end and sides of the 

 larva simply ceases towards the hinder end, and while the 

 flagellated layer is coloured orange, red or scarlet, the inner 

 mass protrudes posteriorly with no other colouring than 

 that of ordinary protoplasm. In the second type the hinder 

 end bears, in the region where the flagellated layer ceases, 

 a circle of especially developed flagella of large size, 

 which are stiffer than the other flagella, and more 

 resemble bristles, and are carried upon a circle of cor- 

 respondingly large cells. In addition to this peculiarity, 

 the cells formine the surface at the hinder end of the 

 larva are pigmented, the large flagellated cells being 

 chiefly, though not exclusively, the seat of this pigment, 

 so that the larva has at its hinder end a violet, brown, or 

 yellow pigment ring, while the rest of the body is white. 

 These differences of ciliation and pigmentation are such 

 as to be easily recognised with a magnifying glass of low 

 power or even with the naked eye. Larva? of the first 

 type have been seen in Esperia, Myxilla, Desmacidon, 

 Clathria, Dictyonella, and Axinella, of the second type 

 in Renie7-a, Chalimda, Gellius, Pachyckalina, and Toxo- 

 chalina. Maas thinks that the characters of these two 

 types of larvae are of systematic value, on account of the 

 constancy with which they occur in various genera, and the 

 fact that they coincide with other structural peculiarities both 

 of the larva and the adult. A classification of the Monaxo- 

 nida found on larval characters would place the families 

 Desmacidonidce and Axinellidce of Ridley and Dendy in one 

 group, and the families Homorhaphidce and Heterorhaphidce 

 in another, in opposition to Vosmaer's classification, which 

 brings together Axinella and Homorhaphidce, on account 

 of their lacking microscleres, while forms such as Gellius 

 are placed with Desmacidon and Myxilla. It is interest- 

 ing to note, however, that though Gellius possesses 

 microscleres in the adult condition, its larva has macro- 

 scleres only and is more nearly related to forms without 



