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 Gymnolcemata, which 

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

 tolmmata* which possess an epistoma, and usually have the 

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

 shaped; whence the term hippocrepian applied to such Po- 

 ly zoa. 



Among the Gymnoleemata are distinguished : the Cyclo- 

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

 opercular structures ; the Ctenostomata (supra), and the 

 Che ilostomata {supra) . 



All the PJiylactolcemata are inhabitants of fresh water ; 

 while all the Gymnolaimata, 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 with cilia. From one end of this cystid, one or more poly- 

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



In the Gymnohematous genera Biic/iila, Scrupocellaria, and 

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

 and with eve-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 2 has showm that the anomalous Cyphonautes, 

 which he considers to resemble Actinotrocho, and which is 

 inclosed in a bivalve shell, is the larva of Membranipora pir 

 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. 



1 See Dumortier and Van Beneden, " Ilistoire Xaturelle d. Polypes compo- 

 ses d'eau douce" ("Mdm. de l'Aad. Royale de Bruxelles," 1850) ; the mono- 

 graph of Allman cited above ; and Nitsche's " Beitrc"i£re." 



2 " Zur Entwickeluncrsoreschichte Und svstematischen Stellung der Bryczoen 

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



