BRYOZOA 249 



embryo develops in the ovary, receiving nutriment directly from the 

 body cavity. 



All ectoprocts develop also asexnally by budding, and thus produce 

 the branching and incrusting colonies which characterize the group. In 

 many species polymorphic zooids appear which differ much from the 

 others in structure and perform certain specialized functions. These are 

 the ooecia, which are brood chambers, above mentioned, the avicularia 

 (Fig. 411, A), birdhead-like structures which seize small animals in 

 their jaws, and are probably defensive in function but also function in 

 keeping the surface of the colony clean, and the vibracula (Fig. 411, B), 

 whip-like appendages which wave about in the water and are also defen- 

 sive. In the fresh-water rJiylactoJamata disc-like buds called statoblasts, 

 which have a hard chitinous shell, develop on the funiculus and either 

 float or drop to the bottom on the death of the animal in the fall of the 

 year or in periods of drought. In the spring or on the return of the wet 

 season each statoblast gives rise to a young colony. 



The Ectoprocta have great powers of regeneration. Periodically in 

 the marine species the soft parts of the animal, with the exception of the 

 body wall, break down and form a single round mass called the brown 

 bodj^ Later new organs develop, the brown body apparently being 

 expelled from the body as waste matter. 



Kidneys have not been certainly demonstrated in Ectoprocta. No 

 blood vessels are present, but a blood fluid fills the body cavity. The 

 nervous system consists of a ganglion between the mouth and anus and 

 nerves radiating from it: in many species no nervous system has yet 

 been seen. No special sense organs are found. The class contains 2 

 orders and the great majority of all Bryozoa. 



Key to the orders of Ectoprocta: 



«! Mostly marine Ectoprocta, with a circular lophophore. . . .1. Gymnol^mata 

 G2 Fresh-water Ectoprocta with a horseshoe-shaped or oval lophophore. 



2. Phylactol^mata 



Order 1. GYMNOLiEMATA. 



Lophophore circular; mouth can usually be closed by a flap called 

 the operculum; vibracula, avicularia, and ooecia often present: marine 

 Bryozoa (excepting the Paludicellidae) including about 1,700 species, 

 which are grouped in 3 suborders. 



Key to the suborders of Gymnolcemata : 

 Ui Opening of zocecium wide and circular and not capable of being closed 



by an operculum 1. Cyclostomata 



a. Opening of zoffioium, when lophophore is retracted, more or less flattened 

 and capable of being closed by an operculum. 



61 Operculum a movable horn-like valve 2. Ciiilostomata 



62 Operculum composed of a fringe of setae 3. Ctenostomata 



