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 Ertoprocta are divided into the Gymnoloeruata^ which 

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

 tolamiata^^ 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 Gymnoloemata are distinguished : the Cyclo- 

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

 opercular structures ; the Ctenostomata {siq)7'a), and the 

 Cheilostomata {sitpra) . 



All the JPhylactolmmata are inhabitants of fresh water ; 

 while all the Gymnolmmata^ except Paludlcella, are marine. 



The polyzoarium of Gristatella 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, w^hich is covered external- 

 ly with cilia. From one end of this cystkl^ one or more poly- 

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



In the GymnolcBmatous genera Bugula., Scrupoeellaria^^ind 

 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 Cyphonautes^ 

 which he considers to resemble Actmotrocha^ and which is 

 inclosed in a bivalve shell, is the larva of 3Iemhrampora pi- 

 losa. It is provided w^ith 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 w^hich a polypide is developed, as in the 

 foregoing cases. 



1 See Dumortier and Van Beneden, " Histoh-e Naturelle d. PoljTies compo- 

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

 graph of Allman cited above ; and Nit>iche's " Beitrage." 



2 *' Zur Entwickeh^nsrso'escliicbte und systematischen Stellung der Bryczoen 

 und Gephyreen." (" Archiv fiir mikr, Anat.," 1869.) 



