20 SPONGLE. 



Phylum I. SPONGI^ (Porifera). Sponges. 



The digestive tract has the form of a much-branched canal-system. 

 Many of the endoderm cells (collar-cells), which may be limited to 

 flagellated chambers, are provided with a flagellmn and collar. Numerous 

 microscopic pores (inhalent or nutritive apertures), and one or more 

 oscula (exhalent apertures). The mesogloea contains sense-cells, con- 

 tractile fibrous cells, supporting cells, skeletogenous cells (together with 

 horny fibres, and calcareous or siliceous spicules), pigment cells, wander- 

 ing cells, ova, and spermatozoa. Asexual reproduction by budding, 

 through gemmules, &c. Sexes mostly separated ; usually viviparous. 

 Thread-cells absent, in contrast to the Cnidaria. Marine, with few 

 exceptions. 



Order 1. Silicospongice (Fibrospongiae, Micromastictora). Usually 

 possess a skeleton of horny fibres, siliceous spicules, or both. Collar-cells 

 small. 



Tetractinellida3 (Lithospongias), siliceous sponges with 4-rayed 

 spicules. Geodia, Monactinellidse. 



Hexactinellida3 (Hyalospongise), 6-rayed siliceous spicules. 

 Euplectella, Venus' flower-basket ; Hyalonema, glass-rope sponge. 



H a 1 i c h o n d r i B, skeleton of horny fibres and siliceous spicules. 

 Reniera, Spongilla fluviatilis, fresh-water sponge. 



Ceratosporigia?, horny sponges. Euspongia officinalis adriatica, 

 bath sponge. 



Myxospongise, gelatinous sponges, without skeleton. Halisarca 

 lobularis. 



Order 2. Caldspongice, calcareous sponges. Grantia, Leuconia, 

 Sycon. 



