Chap. II. GRADATION AMONG ACALEPHS. 115 



the cli^^miferous tuljes terminate iu clifFerent ways in diflFereut genera ; anastomozing 

 in a more or less direct manner with one another around the actinostome. Besides 

 the vertical chymiferous tubes Avhich follow the course of the rows of flappers, 

 there are two other vertical chymiferous tubes, presenting various degrees of com- 

 plication in different genera. These two tubes are placed opposite to one another, 

 in the same direction as the main branches of the whole system. All Ctenophoraa 

 have a decided tendency to a bilateral symmetry, their body being more or less 

 compressed. In some the outline is spheroidal, in others more cylindrical, while 

 in others still, the spherosome expands on the actinal side of the body into wing- 

 like appendages. 



The most prominent peculiarities of the Ctenophora; as an order consist, there- 

 fore, in the complication of their system of chymiferous tubes, in the presence of 

 locomotive flappers on the surface, and in a tendency to a bilateral symmetry, 

 resulting from the inequality of their spheromeres. 



All these peculiarities show distinctly that the Ctenophorse are superior to the 

 Discophoroe ; for in the latter the ch}Tniferous tubes simply radiate from the main 

 cavity towards the periphery, and, when branching, divide in one and the same 

 plane. Moreover, Discophoroe have no rows of locomotive flappers, and move only 

 by the contraction of their spherosome, which assumes the form of a hemispheric 

 disk, spreading uniformly in every direction, without exhibiting the slightest tendency 

 to bilateral symmetry. It is true that in Discophora? the actinostome is apparently 

 more complicated than in Ctenophorte, because it is surrounded by long appendages 

 hanging below the main cavity ; but, notwithstanding this seeming superiority of 

 development, it wiU be shown hereafter that the actmostome of the Ctenophorae 

 is in reality more highly organized than that of the DiscophorJB, although the 

 bulk of its appendages in the latter gives it a greater prominence. It is true 

 also that in a large number of Discophorse the margin of the disk is provided 

 with numerous tentacles, l)ut these tentacles are only peripheric diverticles of the 

 chymiferous tubes, and in no way constitute a higher complication of that system 

 than the vertical branches of the chymiferous tubes of the Ctenophorte with their 

 locomotive flappers. It is true also that the Discophorai have distinct sexes, their 

 ovaries and spermaries fomiing large bunches, in separate cavities, while the Cte- 

 nophorte are hermaphrodites ; but the special arrangement of the ovaries and 

 spermaries in the latter, placed as they are on opposite sides of the vertical 

 branches of the chymiferous tubes, contributes to render the complication of the 

 structure of each individual more apparent m Ctenophoraj than in Discophoroe. 

 It is true also that the Discophoraj have eight, and sometunes twelve or even 

 more distinct eyes at the end of their radiating chymiferous tubes, while in Cte- 

 nophoraa there is a single eye at the abactinal pole ; but then that smgle eye 



