6l2 



THE INVERTEBRATA 



velops into a single individual but always into a large number by what 

 is known as embryonic fission, such as occurs in the parasitic Hymen- 

 optera. A much modified zooecium, the so-called ovicell, serves as 

 a brood pouch and in that the primary embryo is formed and attached 

 to follicular tissue which supplies nourishment. Masses of cells are 

 nipped off to form the secondary embryos each of which becomes a 

 free-swimming larva. 



Fig. 421. Section through an endoproctous polyzoan. Altered from Ehlers. 

 An. anus; at. atrium; ga. ganglion; g.gl. gonad; g.op. genital opening; 

 int. intestine ; M. mouth ; mr. sphincter muscle of circular flap of body wall ; 

 oe. oesophagus ; par. parenchyma ; st. stomach. 



Classification 



Class Endoprocta (Fig. 421). Simple and archaic polyzoa in which 

 the anus is situated inside the lophophore ; without coelom, the 

 space between gut and body wall being filled with paren- 

 chymatous tissue; with non-retractile tentacles which can be 

 covered by a circular flap of the body wall, provided with a 

 sphincter muscle; with a pair of protonephridia ending in flame 

 cells, and gonads with a duct of their own; with a trochosphere 

 larva. Pedicellina, Loxosoma. 



