ILLUSTRATIONS OF COMPARATIVE ANATOMY, 

 VERTEBRATE AND INVERTEBRATE. 



SUB-KINGDOM PROTOZOA. 



1. A piece of the common Freshwater Sponge (Spongilla, 

 fluviatilis), exhibiting its siliceous skeleton. 



Rolleston, p. 163. 



SUB-KINGDOM OELENTERATA. 



CLASS HYDROZOA. 



2. A Sea-Fir (Sertularia abietina). 



It consists of a slender pinnately-branched 'coenosarc' in- 

 vested by a chitinous 'periderm.' Both the main stem and 

 the lateral pinnae are beset by numerous sessile or sub-sessile 

 more or less flask-shaped chitinous ' hydrothecae,' in which the 

 'polypites' are lodged. In addition to these, larger but similarly 

 shaped vesicles are to be observed studding the pinnae. These 

 are the 'gonotbecse' and contain the generative zooids. The 

 animal when mature is non-locomotive and is attached to its 

 base by a ' hydrorhiza.' 



3. A Sea- Anemone (Tealia crassicornis), from which the 

 base has been removed. The tentacles and the space round the 

 mouth ' peristomial disc ' are too much retracted to be well 

 seen. On the other side of the preparation the internal surface 

 of the digestive cavity is exposed, marked with fine radiating 

 lines, which correspond with the attachments to it of the 

 vertical muscular lamellar plates termed 'mesenteries.' These 



CL. 1 



