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 Gymnolmmata, which 

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

 tolcemata, 1 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- 

 lyzoa. 



Among the Gymnolcemata are distinguished : the Cyclo- 

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

 opercular structures ; the Ctenostomata (supra), and the 

 Cheilostomata (supra). 



All the Phylactolwmata are inhabitants of fresh water ; 

 while all the Gymnolcemata, except Paludlcella, are marine. 



The polyzoarium of Cristatella is free and creeps about as 

 a whole ; and that of Lumdites 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 sao. 



In the Gymnokematous genera Bugula, Scrupocellaria, and 

 JBicellaria, 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 give3 rise to the first cell of the polyzoa- 

 rium. 



Schneider 2 has shown that the anomalous Cyphanautes, 

 which he considers to resemble Actinotrocha, and which is 

 inclosed in a bivalve shell, is the larva of Membrayiipora 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. 



1 See Dumortier and Van Beneden, " Histoire Naturelle d. Polypes compo- 

 sees d'eau douce " (" M£m. de l'Aad. .Royale de Bruxelles," 1850) ; the mono- 

 graph of Allman cited above ; and Nitscne's " Beitriige." 



2 " Zur Entwickelungsffeschichte und. systematischen Stellung der Biyozoen 

 und Gephyreen." ( u Archiv fur ruikr. Anat," 1869.) 



