Chap. I. STRUCTURAL FEATURES. 163 



that some Ctenophora^ have a mantle, which is wanting in others, is incorrect. 

 As we shall see in the sequel, the lobe-like appendages of the anterior and pos- 

 terior spheromeres of some representatives of this order are direct prolongations 

 of the spherosome, over which the rows of locomotive flappers are extended, and 

 to which they bear the same relations as in the more spheroidal or more cylindrical 

 forms. The chymiferous tubes also extend uninterruptedly into these lobes, in the 

 same manner as they extend into the peripheric parts of the plainest species. So 

 that, whatever be the general form of the spherosome, it is one and the same 

 body in all Ctenophora3. Again, whatever be its form and size, the Ctenophoraj 

 have all a compressed digestive cavity, trending in the same plane as the circum- 

 scribed area of the abactinal pole, and at right angles with the intermediate 

 chymiferous tubes ; and in all, that cavity is broadest towards the mouth and tapers 

 in the opposite direction, its lateral walls being flattened against one another when 

 it is empty. The narrow abactinal opening of the digestive cavity opens directly 

 into the centre of the chymiferous system, which in all Ctenophoroe has a very 

 peculiar mode of ramification, the general outline of Avhich agrees in all, though 

 marked peculiarities ma}' be noticed in its details in different fimilies. The most 

 striking and characteristic features of this chjaniferous system, when contrasted with 

 that of the other Acalephs, consist in its bilateral symmetry, the axial funnel-like 

 prolongation of its central portion, into which the digestive cavity opens directly, 

 and the presence of two asymetrical openings at the abactinal pole, through which 

 it discharges its contents. 



Immediately be3'ond the alsactinal opening of the digestive cavity there arise 

 two main trunks of the chymiferous system, in opposite directions one from the 

 other and at right angles with the plane of the digestive cavitj'- ; so that the 

 main stems extend right and left, and almost horizontally, into the spherosome. 

 Before dividing, each trunk sends off a vertical branch along the adjoining sides 

 of the digestive cavity, and then divides into two nearly horizontal branches, which 

 soon divide again; so that each trunk has four nearly horizontal or slightly incUned 

 forks extending to the periphery, where they open into as many vertical branches, 

 Avhich converge in opposite directions toward the actinal and the abactinal poles. 

 The further course of these vertical peripheric branches varies with different families ; 

 but, as far as I can ascertain, all CtenophorjE have a chymiferous tube upon each 

 flat side of the digestive cavity; in all, the two main trunks divide into four forks; 

 and these eight forks open in all into eight vertical peripheric chymiferous tubes; 

 and in addition to these, there are, in some families, other vertical and lateral 

 chjTniferous tulies arising between the lateral horizontal forks of the main trunk, 

 which again vary in their ultimate relations in diftereut families, lateral tentacles 

 existing in some, and being absent in others. All these tubes, whatever be their 



