12 CTENOPHORES OF THE ATLANTIC COAST OF NORTH AMERICA 



dseum also is wide and flat and is between one-half and one-third as long 

 as the long axis of the ctenophore. The funnel-cavity, or mid-region of 

 the central entodermal part of the gastric system, sends out 2 wide 

 paragastric branches, and also 2 canals to the bases of the tentacles, and 

 it also gives rise to 4 interradial side branches, each one of which 

 bifurcates, thus giving a canal to each of the 8 rows of ciliated plates. 

 The gelatinous substance is transparent and glassy, while the tentacles 

 and stomodaeum are milky, or dull orange yellow or brownish orange. 



Fig, 5. — Pleurobrachia pileus; view looking down upon apical sense-organ 



at aboral pole of the animal. 



Lettering as in fig. 4. e, ova in meridional canals under ciliary combs; 5, sensory 

 tracts from apical sense-organ to rows of combs; to, opening of tentacle-sheath. 



The development has been studied by A. Agassiz, 1865, 1874. In 

 common with that of other ctenophoras, it is a simple metamorphosis. 

 When young the tentacular diameter is about twice as great as the sagit- 

 tal and the body is thus compressed laterally as in Mertensia. The combs 

 of cilia make their appearance as 4 double rows of simple, hair-like lashes; 



