srox<;i!i>\. 



30 ( J 



Dysidea, Totrochota, RhcvpMdophlm, Aeanihella). In the systematic 



descriptions of the genera and species I have employed the old 

 expression "sarcode'' for the sofl tissues generally, as being intel- 

 ligible, comprehensive, and as having the advantage of involving no 



special theory or view with regard to the homologies of the parts 

 referred to; the greater part of the tissues included under the term 

 are, however, the "mesoderm" of F. E. Schulze, together with the 

 ciliated chambers and the walls of the canal-system which it 

 encloses. 



Individual Variation. — A few remarks on this subject are sug- 

 gested by the study of this large collection. First, variation in the 

 size of spicules is an almost invariable occurrence in different speci- 

 mens of the same species, as it is in individual spicules in the same 

 specimen ; in the one ease, however, it rightly falls under the head of 

 variation, in the latter chiefly under that of growth. In the descrip- 

 tions below will be found statements which show the range of this 

 form of variation within the limits of a species to be frequently 

 wide, see especially Leueophloeus fenestratus, Echinodictyum (the 

 spined spicule), and Stelletta purpurea. The Ectyonidse exhibit, 

 as a rule, surprisingly little variation of this kind, and little use is 

 to be made of characters based on size in distinguishing even species 

 in this group. Chalinidae and Desmacidinidae are also very fairly 

 constant as a rule. Secondly, variation in the form of spicules is 

 less common. The Suberitidae exhibit variation of the head of the 

 skeleton-spicule from sub-acuate to spinulate (Suberites). Modifi- 

 cations of the form of the ends of acerate spicules are certainly not 

 often to be noticed ; but this collection shows that in Pellina muricata 

 the ends of the acerate vary from being gradually sharply pointed 

 to being rounded off almost as thoroughly as in the usual " cylin- 

 drical;" and in Cladechalina nuda the ends may taper gardually 

 from about four diameters from end of spicule, or else from within 

 about 1| diameters (var. abrwptispicula, mihi), producing a very 

 different appearance. Thirdly, as to variation in the external form 

 of the Sponge within the limits of the same species, striking ex- 

 amples are afforded by the series of Iotrochota purpurea and Claihria 

 p inwardti (where a multi-personal origin appears to explain the most 

 remarkable case). The number of vents present has been used as a 

 generic character in the Tetractinellida by Prof. Sollas (Geodia, 

 Isops). In one of the species of Stelletta here described this seems 

 to be constant, in the other not ; in the species of Geodia described 

 below it is doubtful whether absence of vents (" lipostomy,'' HdcJcel) 

 is constant. 



"Person ,: -theoi'y. — The individuality of those parts of a Sponge 

 which enclose a single cloacal cavity seems to be regarded as a fact 

 by Marshall, who speaks (Zeitschr. wiss. Zool. xxxv. p. 98 &c.) of 

 species of Dysideida? as being " monozoisch " or " polyzoisch." It is 

 difficult to see how the different cloacal tubes which are formed 

 during adult life by folding-over of a flat wall, as appears to be the 

 case in the species named below, SipTionochalina bullata and Dysidea 

 semicanalis, can be said to constitute individuals. It seems possible 



2b 



