324 



ZOOLOGY 



SECT. 



i 



been already described in the case of Bugula. In some 

 Ctenostomata there is in addition a thick-walled chamber 

 the gi','.iu-d with chitinous teeth, between the ossophagus and 

 stomach. 



The nervous system consists of a single, sometimes bilobed, 

 ganglion (Fig. 258, gang, and Fig. 25!), get) placed between the 

 mouth and the anal aperture, and nerves passing from it to the 

 various parts. There are never any organs of special sense, unless 

 the epistome of the Phylactolsemata be of that nature. 



Nephridia are not known with certainty to exist in any of 

 the Ectoprocta. In some there is a pore through which water 

 enters the body-cavity : or a ciliated intcrtcntacular title opening 

 at the base of the tentacles. In Cristatella there is a pair of 



ciliated canals with funnel- 

 like internal apertures and 

 opening on the exterior by a 

 common bladder-like excre- 

 tory duct, and similar ciliated 

 tubes occur in other Phylac- 

 tolsemata. 



Excretion appears to be 

 performed by certain cells 

 of the funicular tissue and of 

 the parenchyma or ccelomic 

 epithelium. These become 

 loaded with the products of 

 excretion, and become free 

 as leucocytes in the ccelome, 

 whence they probably pass 

 out through the interten- 

 tacular tubes or ciliated 

 canals. 



In many Ectoprocta the 

 colony bears a series of re- 

 markable appendages - - the 



avicularia which are of the nature of modified zooids. In 

 tvpical cases the avicularium has the bird's-head-like form that 

 has been already described in the case of Bugula ; sometimes it 

 is completely sessile. A second set of movable appendages found 

 in some forms are the vibracula : these are long tapering whip- 

 like appendages which execute to-and-fro movements. The avicu- 

 laria are frequently found to have seized in their jaws minute 

 Worms or Crustaceans, and it is probable that their function, as 

 as that of the vibracula, is defensive : in the case of the 

 'i-ii'trv, which form unattached colonies, the movements of the 

 vibracula subserve locomotion. 



The impregnated ova in many cases undergo the early stages of 



&- 



Fie,, -jr.;!. Anterior portion of the body of 

 Lophopus from the right side. an. anus; 

 ep. epistomu : <'.. ganglion; o. mouth; pr. in- 

 Te^tiiic : xt. (.esophagus; t. tentacles cut off 

 ne.ir the Viuse. (From Lang's Text-Book.) 



