324 



ZOOLOGY 



SECT. 



been already described in the case of Bugula. In some 

 Ctenostomata there is in addition a thick-walled chamber 

 the ghzard with chitinous teeth, between the ossophagus and 

 stomach. 



The nervous system consists of a single, sometimes bilobed, 

 ganglion (Fig. 258, gang, and Fig. 259, yd) 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 Phylactolaemata 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 intertentacular tube 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- 

 tolaemata. 



Excretion appears to be 

 performed by certain cell 

 of the funicular tissue and o 

 the parenchyma or ccelomi 

 epithelium. These becomi 

 loaded with the products o 

 excretion, and become fre< 

 as leucocytes in the ccelome 

 whence they probably pas 

 out through the interten 

 tacular tubes or ciliate( 

 canals. 



In many Ectoprocta th 

 colony bears a series of re 

 markable appendages th 

 avicularia which are of the nature of modified zooids. Ir 

 typical cases the avicularium has the bird's-head-like form tha 

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

 is completely sessile. A second set of movable appendages fouiic 

 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 minut 

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

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

 Selenariidce, which form unattached colonies, the movements of th 

 vibracula subserve locomotion. 



Tin- impregnated ova in many cases undergo the early stages of 



FIG. 259. Anterior portion of the body of 

 Lophopus from the right side. an. anus ; 

 c/i. epistome ; pa. ganglion ; o. mouth ; pr. in- 

 testine ; st. oesophagus ; t. tentacles cut off 

 near the base. (From Lang's Text-Book.) 



