288 SYNOPTIC COLLECTION. 



some of the species (Nos. 711-721). These illustrate 

 different modes of growth in colonial forms. Cellularia 

 ( No. 711, C. rigida) is an erect species with its many 

 branches made up of joints. The beautiful Catenicella 

 (No. 712) has delicate curling branches, while Bugula 

 (No. 713) is tree-like in form and some species show a 

 spiral mode of growth. Peculiar modifications of struc- 

 ture are found in these specialized Polyzoa, such as the 

 birds' heads or avicularia, which are remarkable organs 

 of uncertain function. 1 The avicularia are well illustrated 

 by Bugula when seen under the microscope (PI. 714). 

 One avicularium (b) is seen with jaws closed, and another 

 (b') with the lower jaw open. These little organs have 

 been seen to catch small animals. 



Biflustra perfragilis (No. 715) is an extremely fragile 

 specimen growing in a circular form. In Tessaradoma 

 (No. 716, T. magnirostris) there is one layer of zooecia, 

 while in Adeona (No. 717, A. grisea) the zooecia are in 

 two layers. In general form Adeona resembles the fan 

 coral, Rhipidogorgia. The colony is attached by a 

 slightly flexible stem, but in Adeonellopsis (No. 718, A. 

 australis) there is a rigid base. 



Lepralia (No. 719) forms a large colony, and the flat- 

 tened branches unite irregularly. In Filogrina (No. 



720, F. implexd) the branches appear to be made of 

 strands. 



Among the fresh-water Polyzoa are Retepora (No. 



721, R. phoenicea) and Cristatella. The latter has the 

 power of locomotion, though it is probably descended 

 from some marine stationary form. 



ANNELIDA. CHAETOPTERA. 



The record left by the early ancestors of our present 

 worms is scanty and unsatisfactory. It offers another 



1 Hertwig, Man. Zool., transl. by J. S. Kingsley, 1902, p. 323. 



