io8 Introduction to Animal Morphology. 



They are hermaphrodites, and the sexual products 

 arise in folds or pouches of the radial canals, the ova 

 at one side, and the spermatozoa at the other. The 

 ova are expelled by the mouth at all seasons of the 

 year, and develop usually with no metagenetic forms. 

 At first only four ctenophores exist, as in the non- 

 ciliated Eucharis ; some may have a larval stage, such 

 as the Cellephobe oi Busch. In development the cte- 

 nophoral canals arise as offshoots from the endoder- 

 mal cavity, and the gastro-vascular lobes appear at 

 first as solid cellular cords. There may be also in 

 the embryo provisional oral lobes, &c., like the per- 

 manent auriculae of some forms. 



There are over one hundred species, mostly small ; Chia- 

 jea being the giant of the sub-class. They are distributed in 

 four orders. 



1 . Eurystomata (Zf;^c/('rtr/) — oval, wide-mouthed, with no 

 appendages, and a circum-oral canal. This includes the 

 families Beroidae, with entire margins at each pole, the apical 

 end being either conically extensile (Beroe), . or not (Idyia) ; 

 Neisidse with a compressed apical pole, which is deeply 

 notched, and unequal ctenophores ; Rangidoe with a deeply 

 notched oral pole. 



2. Saccatae {Agassi'z) — no circum-oral vessel; tentacles 

 two, turned from the mouth ; ctenophores sub-equal or equal. 

 The families are : — Pleurobrachid^, with no lateral folds, 

 and a symmetrical, round, or oval body, having the cteno- 

 phores reaching from pole to pole (Pleurobrachia), or only 

 l or f of the meridian, and the tentacles with simple 

 (Eschscholtzia), complex (Hormiphora) or no appendages 

 (Dryodea) ; Mertensidae have broad, often heart-shaped, 

 bodies, with unequal ctenophores and simple tentacles 

 (Haeckelia), or equal ctenophores prolonged on processes at 

 the apical pole (Gegenbauria), or with rounded sides (Mer- 

 tensia) ; Callianiridas are cylindrical, winged at the oral pole. 



3. Taeniatae (Agassi'z) — ribbon-like, with no oral lobes; 

 tentacles two, turned to the mouth. There is one family. 



