Chap. III. GENUS IDYIA. 279 



to move all together {Fig. 2). The appearance of the flappers themselves when 

 in different states of expansion and contraction also varies greatly, and hence the 

 different aspects of Fif/s. 1 and 2 in PI. I. and PI. 11., though they represent identical 

 attitudes, Fig. 1 of PI. I. corresponding to Fig. 2 of PI. II., and Fig. 1 of PI. II. 

 to Fig. 2 of PI. I. Magnified figures (PI. H. Figs. 4, 5, 11, 12, 13, 14, 15, 16, 17, 

 and 18) illustrate these differences still more clearly. In a state of rest, or during 

 slow ^progression, the combs have their cilia nearly straight {Fig. 11), and bent 

 toward the actinal side of the body. When raised into action they curve, gently 

 if the motion is moderate {Figs. 13 and 15), and more strongly if the action is 

 more energetic {Figs. 12 and 16). 



The relations of the locomotive flappers to the ambulacral tubes and to the 

 ovaries and spermaries are more easily traced in our Idyia than in any other 

 Ctenophorse I have seen. Facing the surface (PI. I. Fig. 3 and PI. 11. Fig. 4), 

 nothing can be more evident than that the pouches on the two sides of the ambu- 

 lacra are not identical, and also that identical pouches are never on the same side 

 of adjoining ambulacral tubes; for pale pouches face another in Fig. 4, and both are 

 ovarian sacs, while those on the other side of the ambulacral tube, the spermatic 

 pouches, are almost entirely concealed by the crowded deep pink pigment cells. 

 Now the same parts seen in profile (PL II. Fig. 13) show the vmdeveloi^ed sexual 

 pouches to be diverticula of the ambulacral tubes, which retain the same relations 

 to the chymiferous tubes and the locomotive flappers after they have completed their 

 growth and are full either of spermatic particles {Fig. 11) or of eggs {Fig. 16). 

 This close connection of the sexual organs with the ambulacral tubes and the loco- 

 motive flappers is one of the most interesting features of the structure of the 

 Ctenophorte, because, in my oj)inion, it shows the close homology which this appa- 

 ratus presents with the ambulacral system of Echinoderms, and especially with that 

 of the Crinoids with their egg-bearing pinnute uj)on the sides of the ambulacral rows. 



There is hardly any thing among Acalephs equal in beauty to the iridescence 

 of the locomotive flappers of our Idyia, playing with all the colors of the rainbow 

 between the rosy edges of its ambulacral zones. Beyond the rows of locomotive 

 flappers on the abactinal side, eight narrow bands {Fig. 3) may also be seen 

 extending to the base of the central eye-speck. These bands consist of slight, 

 immovable projections accompanied by pigment cells. Those extending from the 

 anterior and posterior pairs converge toward the sides of the circumscribed area, 

 which they follow to the eye-speck, while the lateral ones extend straight to the 

 same point. The course of these bands to the very base of the central eye-speck 

 is well shown in our Idyia (PI. II. Figs. 3, 8, 9, and 18), and more easily traced 

 than in Pleurobrachia and Bolina. 



The circumscribed area forms a prominent feature of the abactinal pole, being 



