Introduction to Animal Morphology. 229 



growth of the embryo in Rhabdopleura there are two fleshy 

 side lobes attached along the dorsal edge, which do not in- 

 crease as growth progresses, and are supposed by Allman to 

 be the homologues of the mantle lobes of lamellibranchiate 

 Molluscs. Rounded germ capsules are found inside polypide 

 cells (zooecia), of which the original inhabitant has died. 

 These are formed from protoplasmic masses below the fundus 

 of the stomach, and originate new inhabitants for the deserted 

 house. A second rarer way for new inmates to arise is by 

 budding from the endocyst. 



About 600 species exist, divided into two orders : 

 i. Gymnolaemata (AH man) with no epistome, a funnel- 

 shaped mouth, and the 9-16 tentacles on a circular lopho- 

 phore ; they never develop statoblasts. This includes six sub- 

 orders : 



Sub-order i. Cyclostomata calcareous, porous, each per- 

 sona retractile into its cell ; mouth terminal, wide ; avicularia 

 and vibracula none; cell-mouth with 'no crown of bristles ; 

 are mostly fossil (Mesozoic) ; some have a jointed, 

 colonial axis (Crisiadae) ; others are unjointed, and with 

 .ila to the cells (Myriozoidas) ; the cells may have thin 

 mouths, separate, protruding (Tubulata), or united in project- 

 ing bundles (Fasciculata). 



. Ctenostomata retractile, with terminal, wide 



mouth, and no avicularia nor vibraculaj the oval or cylindrical 



cells not pillared, but though separate, arising from a common 



: cell mouth with a setose margin for its closure. The 



colony may be horny and crust-like, freshwater, each cell joined 



_, r hbour cells (Hislopiada:, a passage form), or they 



'iigy, massive, or crust-like ; the imbedded 



with contractile mouths (Alcyonidiadae), or plant-like 



rms, upright or creepin-, with projecting 



Ifl always present in \\->iriilariadae. 



. C'hilotomata lophophorr and sheath pro- 



nioulh narrower than the cell, placed at the 



iiinal pole; innith often with a horny 



uliim, or a sphin ilia and vilr.eula often 



pini; 

 organs (Selenariachu) ; the colony in the other fami! 



