178 CTENOPHOR.E. Part II. 



brought into view. In the attitude in Avliich Gegenbaui- has represented his 

 Eurani[)hiva vexilUgera, they cover one another, as they then he in the same phiue. 

 In order readily to designate these two tulK's, which are eminently characteristic 

 of the Muemiida3 or Calymnidce, I shall hereafter designate that which follows 

 closely the outline of the digestive cavity as the stomachal or coeliac cliymifcrom lube, 

 and call that Avhich lies outside,, the infcrambulacral or tentacular cJa/miferoiis tube. Now, 

 the structural peculiarity of the Beroids proper consists in having a very large 

 stomachal or coeliac chymiferous tuljc opening into an equally Avide oral tube 

 (PI. II. F'kj. 10), wliild the iiilcrambulacrcd or tentacular tube is cntirelij wanthuj. The 

 centre of the whole chymiferous system, its main trunks and the axial funnel, is 

 remarkably small in comparison to the wide ambulacra!, coeliac, and oral tubes. 



There are other secondary anatomical peculiarities, equally characteristic of this 

 group, which may now be mentioned also. The eight ambvdacral chymiferous tubes 

 are equally developed ; there is no diflerence in the extent or size or structure 

 of those running along the sides, or along the anterior and posterior surfaces ; 

 they all give out numerous, rather conspicuous, and highly ramified branches, while 

 the cceliac tube is entirely destitute of ramifications. The ovaries and sjjermaries 

 (PI. II. Fhj. 4, and PL I.), the special arrangement of which has already been 

 described above, are large and very conspicuous at the spawning season. The 

 circumscribed area (PL I. Fkj. 3, and PL II. Fig. 9) is encircled Ijy a ptrominent 

 wall of elegantl}^ branched fringes. 



The structural character bearing more directly upon the form of this gi'oup of 

 Ctenophoraj consists chiefly in the even thickness of the sphcromere (PL I. Figs. 

 3 and 4), which i-enders it movable in every direction ; so that the changes of 

 outlines of the Beroids proper are far more extensive than those of any other 

 members of the whole order. This ability to change their form is further enhanced 

 in these animals by the circumstance, that the digestive cavity extends so far 

 towards the abactinal pole as to reduce the bulk of the spherosome in that 

 direction to the average thickness which it has iq^on the sides. A conqiarison of the 

 different figures of PL I. may give some idea of these changes of form; and Fig. 10, 

 especially, which represents a specimen of the same size as Figs. 7 and S gorged 

 with a Bolina nearl_y of its own size, will show to what extent they may be 

 distended. Fig. 5 represents a specimen with the actinostome turned inside the 

 digestive cavity. Notwithstanding this remarkable movability, all these animals 

 preserve a very regular and symmetrical form in a state of rest, the sides a2)pearing 

 uniformly compressed. 



Thus Ave liaA'e here two difterent categories of characters : first, anatomical 

 peculiarities of the same kind as those upon Avhich the order of Ctenophonx; is 

 founded, only relating to certain limited points of their structure ; and, secondlj^, 



