260 CTENOPHOR^. Part II. 



meut, that is to say, they form a crest projecting outward along tlio tii)»e. If 

 this view of the small lobes is correct, we may consider the vertical In-anch or 

 fork of the chymiferous tube, which extends beyond the auricles toward the corners 

 of the mouth, as the direct prolongation of the ambulacral tulie proper, and the 

 fork which diverges into the large loljes as the anastomotic fork connecting the 

 ambulacral tubes all round the bod}-. The horizontal branches along the sides of 

 the mouth should then be considered as the anastomotic branches between the 

 two lateral amljulacral tubes of each side, and thus the circle would ]je made 

 perfect. 



With these fiicts respecting the structure of our Bolina before us, we are pre- 

 pared to take another and not less instructive view of its peculiar synnuetry, which 

 may lead to a fuller insight into the characteristic features of Radiata. Not only 

 are the two anterior and the two posterior spheromeres different in their develop- 

 ment from the two lateral pairs, but they stand also in peculiar antitropic relations 

 to one another. In the first place, the large lolies, each considered as a whole, 

 are antitropic to one another, that is to say, they bend in opposite directions 

 toward the vertical axis ; and every point of the symmetry presented in a lateral 

 view of the animal arises from this even balance of the anterior and posterior 

 parts of the body, as seen in Fig. 88. But each lobe again consists of antitropic 

 halves ; or, in other words, the two spheromeres which form one lobe are as truly 

 antitropic to one another as the two lobes themselves, for the outlines of the lobes 

 as well as tlie course of their chymiferous tubes are evenly balanced, as Fif/. 89 

 shows. The same is true of the lateral spheromeres : for here those of the same 

 side, as seen in Fig. 88, are antitropic to one another, not only in their general 

 outline, but more especially in the relative position and antagonistic movements 

 of the auricles ; and yet these adjoining spheromeres do not form a pair together, 

 but stand again in antitropic relation to the lateral spheromeres of the opposite 

 side, as Fig. 90 may show. Such a symmetry exists nowhere among bilateral 

 animals, and appears to me one of the most striking peculiarities of the Radiates. 

 Again, the opposite poles of the vertical axis exhiljit the most striking contrasts, 

 both in their differences and their antitropy, for the spheromeres converge as well 

 toward the aetinal as toward the abactinal area, though the two are occupied 

 by diflerent oi'gans, or by identical parts unequally develojjed. A comparison of 

 Figs. 90 and 91 may show at a glance the correspondence and the difl'erence. 



There is a great interest connected with a further investigation of the vibrating 

 cilia of the small lobes, in comparison with the locomotive combs of the amijulacra. 

 The former being ver^' similar to common vibratile cilia, and the latter forming 

 a more complicated system of locomotive organs, while Ijoth are morphologically 

 fully homologous, it follows, that, in a series of structural complications, the loco- 



