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



Order VII. Leucospongle (Syconidse, Leuconidse, and Tichonidae). — Calcisponges 

 without spongiu-skeleton, with vesicular canal-system. 



Order VIII. Pharospongle (Pharetronidae). — Calcisponges with a fibrous spongin- 

 skeleton, with vesicular canal-system. 



Position of the Sponges in the Animal Kingdom. 



The important question of the natural affinities of the sponges and of their position 

 in the animal kingdom has been fully discussed in the former Reports of this series 

 already quoted, and especially in the excellent Report of Sollas on the Tetractinellida. 1 

 Agreeing in general with the deductions of Sollas, as well as with his general conceptions 

 of the sponge organisation, it seems to me not necessary to separate the Spongige from 

 the other Metazoa. The fact that the sponges develop from a true Gastrula, and their 

 tissues from two primary germ-layers, as in all other Metazoa, seems to prove the validity 

 of their position within this kingdom. This position is mainly maintained by 

 Lendenfeld in his works above quoted (1886). The same opinion is confirmed afresh if 

 we look upon the flagellated chamber as the primitive individual, and as homologous 

 with a Gastrsea on the one hand and with a simple Hydroid on the other. I agree with 

 Sollas that the sponges form a separate phylum within the sub-kingdom Coelenterata, 

 but the distance between them and the Cnidaria (especially the Hydroida) is not greater 

 than that between the Cnidaria and the Platoda. The general results of this Report on 

 the Deep-sea Keratosa seem to confirm this opinion. 



The position of the sponges in the animal kingdom (as a separate phylum of the 

 Ccelenterata), which in the present state of our daily increasing knowledge seems to be 

 the most natural, will be best understood from the following synopsis of the Metazoa, 

 which I have employed in my lectures during recent years : — 



Systematical Synopsis of the Main Brandies, Phyla, and Classes 



of the Metazoa. 



A. First main branch of the Metazoa. 



Cmlenteria (Ccelenterata vel Zoophyta). 



Phylum I. Gas thread a. 

 Classes : 1. Physemaria ; 2. Cyemaria (Orthonectidas, Dicyemidse). 



1 Zool. C'hall. Exp., pt. Lxiii. vol. xxv. p. cxii. 



