180 CTENOPIIOR.E. Part II. 



laiuificatioiis. But Avliile the pcriphoric part of the olijniiiorous .sy.stem i^i thus 

 liuiiteil, its contral part is more I'ully developed than iu any other Ctenophora;; 

 the main trunks and their eight forks are very hirge, and the axial funnel is 

 equally ^vide. The most conspicuous structural feature of the Cydippida; consists 

 in the presence of two e.vteimve tcniacular organs, one on each side, attached at tlie 

 bottom of a deep sack, along the proximal surface of which extend two lurc/e puruttcl 

 chumifcrons tubes, homologous to the one simple interandndacral tube of Bolina, 

 alreadj' mentioned aljove. The chief differences in the distribution of the chy- 

 miferous system of the Beroida> and Cydippida? consist, therefore, not only in the 

 limitation of its peripheric branches, the absence of an oral tube, and the broad 

 develo]inient of its centre, Init also in the presence of a double interamliulacral 

 or tentacular tube on each side. The ovaries and sperniaries are very small in 

 comparison to those of the Beroida\ and the circumscribed area of the abactinal 

 pole, covered with vibratile cilia, is simply limited Ijy a narrow ridge. The deep 

 and wide sac containing the tentacular apparatus, and the bilateral disposition of the 

 main trunks of the chymiferous tubes, condjined with their ample dimensions, have 

 a powerful influence in controlling the form of these animals. But we shall 

 consider this point more fully when discussing the characters of the different 

 families of Cydippida?. 



The sul>order of the Mnemiida^ is at once distinguished by the lutvqiud de- 

 velopment of the amlndacrid tiilws and of the tocoinotire Jta/ipers, and l.iy the presence of 

 two more or tess e.vteuslec l<>I>es, formed by a peculiar expansion of the spherosome. 

 Of the eight amlndacral tuljes there are four, the two lateral pairs, which are 

 autitropically symmetrical to one another and identical in form and extent with 

 one another, but differ greatly from the four others, the anterior and the posterior 

 pairs, though these are also synnuetrical and identical among themselves. When 

 contrasted Avith one another, these two sets of tubes present very peculiar combi- 

 nations. In the first place, the anterior pair, which faces tlie posterior pair, or 

 vice versa, is separated from the latter by two i)airs of lateral tubes, so arranged, 

 howevei-, tliat one tube of each pair is on one side, and the other tube of each 

 pair on the other side, of the coeliac diameter or plane, wdiich may divide the 

 anteiior as well as the posterior pair of tubes into equal halves; and not so 

 placi'<l that one pair would be on one side and the other pair on the other side, 

 though at first sight it would seem as if four pairs of tubes w^ere placed crosswise 

 to one another. A correct appreciation of the peculiar synnnetry of the Cte- 

 nophorai is s(j difficult, that, even at the risk of being tedious, I must try to 

 make clear the arrangement of these tuljcs l)y another explanation. Calling one 

 side (lie right, the other tlie left side, and one of the connecting surfiices the anterior 

 and tlie other the posterior, we find that one of the tubes of the anterior pair 



