20 INVERTEBRATE ZOOLOGY. 



B. METAZOA. 



Division I. PROTAXONIA. 



Type I. PORIFERA. 



Class I. Calcispongiae Spicules calcareous — structure of sponge 



comparatively simple. 



Order 1. Asconida Wall of sponge not folded — main cavity 



lined with digestive cells, -^f Ascetta. 



Order 2. Syconida Wall of sponge forming oblong chambers 



opening directly into the main cavity. 

 Digestive cells confined to the chambers. 

 ■^ Sycandra. 



Order 3. Leuconida .Wall of sponge with a very thick meso- 

 derm, in which are spherical chambers 

 lined with digestive endodermal cells 

 Chambers connected with the exterior 

 and with the main internal cavity by 

 branching canals. 



Class II. SiLiciSPONGlAE Spiciiles silicious, sometimes woven to- 

 gether like threads. 

 -^ Euplectella, Spongilla. 



Class III. Keratospongiae No spicules, skeleton a mesh-work of 



woven threads, or wanting. 

 •^ Euspongia. 



Type II. Cnidaria {Coelenterata). 

 Class I. Hydrozoa 



Order 1. Authydrae. 



.Polyp form [Hydrula] without mesente- 

 ries, only in a few instances prodvicing 

 coral. Medusa form {Craspedota) gener- 

 ally small, with velum, 4-8 radiating ca- 

 nals, uncovered sense organs, generally a 

 long manubrium and no genital pouches. 

 Marginal lobes wanting. Gelatinous mid- 

 dle layer without cells. 

 .Sexual cells produced by polyp-form. 

 No medusa generation (free or reduced). 



