THE POLYZOA. 395 



parent buds are really one of two kinds of embryos devel- 

 oped from the impregnated ova. The other kind of embryo 

 becomes a gastrula, with a large post-oral ciliated disk, like 

 a mesotrochal annelid larva, and its ultimate fate has not yet 

 been traced. 



The Ectoprocta are divided into the Gymnoloemata, wliich 

 have a circular lophophore, and no epistoma ; and the FhyUiC- 

 tolmmata,^ which possess an epistoma, and usually have the 

 lophophore prolonged into two lobes, so as to be horseshoe- 

 shaped ; whence the term hippocreplan applied to such Po- 

 lyzoa. 



Among the Gymnolmmata are distinguished : the Cyclo- 

 stomata, in which the ojDening of the cell is round and has no 

 opercular structures ; the (Jtenostomata {siq)ra)j and the 

 Cheilostomata isiqyra). 



All the Phylactolmmata are inhabitants of fresh w^ater ; 

 while all the Gymnolmmata, except Paludlcella, are marine. 



The polyzoarium of Cristatella is free and creeps about as 

 a whole ; and that of Lunulites is free, at any rate in the 

 adult condition. 



In the fresh-water Polyzoa., the impregnated ovum gives 

 rise to a saccular planuliform embryo, which is covered external- 

 ly wdth cilia. From one end of this cystkl, one or more poly- 

 pides are developed from thickenings of the wall of the sac. 



In the Gymnol:iematous genera Piigula, Scriqjocellaria^ and 

 Picellaria, the embryo is ciliated, and provided with a mouth 

 and with eye-spots. After swimming about for some time, it 

 loses its cilia, fixes itself, acquires a chitinous outer coat, and 

 becomes a mere sac or cystid, in which a polypide is developed 

 by gemmation, and gives rise to the first cell of the polyzoa- 

 rium. 



Schneider'* has shown that the anomalous Cyphonaiites, 

 which he considers to resemble Actinotrocha, and which is 

 inclosed in a bivalve shell, is the larva of Memhranipora pi- 

 losa. It is provided with an intestine, and with largely de- 

 veloped ciliated motor bands. But when it attaches itself, all 

 these organs disappear, and the larva passes into the condi- 

 tion of a cystid, from which a polypide is developed, as in the 

 foregoing cases. 



^ See Dumortier and A^an Beneden, " Histoh-e Naturelle d. Pol^-pes compo- 

 s^esd'eau douce " (" Mem. de I'Aad. Royale de Bruxelles," 1850)'; the mono- 

 graph of Allman cited above ; and Nitsche's " Beitraare." 



2 *' Ziir EntwickeUinnrssceschichte und s^'stematisehen Stellung der Biyczoen 

 und Gephvreen." (" Archiv fur mikr. Anat.," 1869.) 



