352 ZOOLOGY MOT. 



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 intertentacular tube opening 

 at the base of the tentacles. 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 are set free as leucocytes in the ccelome, whence 

 they may pass out through the intertentacular tube or may 

 accumulate in the cells of the brown "body. 



In many Ectoprocta the colony bears a series of remarkable 

 appendages the avicularia which are of the nature of modified 

 zooids. In typical 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 avicularia are frequently found to have seized 

 in their jaws minute Worms or Crustaceans, and it is probable 

 that their function, as well as that of the vibracula, is defensive ; 

 in the case of the Selenariidce, which form unattached colonies, it 

 is said that the movements of the vibracula subserve locomotion. 



The impregnated ova in many cases undergo the early stages of 

 their development in certain dilatations of the colony (Fig. 276, 

 oac.\ and in many of the GymnolaBmata (Cheilostomata) these 

 ovicells or occcia, as they are termed, take on a very definite 

 shape. 



Reproduction and Development. As a general rule the 

 Ectoprocta are hermaphrodite. Both ovary and testis are derived 

 from the layer lining the ccelome (parenchyma or coelomic 

 epithelium as the case may be), or from the funicular tissue. The 

 testis may be single or double. The spermatidia, as in Bugula, or 

 the mature sperms, become free in the coelome. The ovary is very 

 generally situated towards the oral end or about the middle, the 

 testis towards the base. The mature ova escape into the coelome, 

 and in some forms there become impregnated apparently by the 

 spermatozoa of the same individual. The development of the 

 larva may take place in the ccelome or in a special diverticulum of 

 it ; in the Cheilostomata the fertilised ova pass into the ovicells ; 

 in some 'cases, both among the Phylactolsemata and the 

 Gymnolsemata, they are received into a sheath formed by the 

 tentacles of an imperfectly-developed zooid formed in a zooecium 

 in which the original zooid had undergone degeneration. 



In those cases in which the early stages of development are 

 passed through in the body-cavity of the parent, the ciliated 

 embryos may either escape through the zooecial aperture after the 



