280 CTENOPHORiE. Part II. 



circumscribed by uprigbt branching fringes dotted with many pigment cells (PI. I. 

 Fkj. 3 ; PI. II. F'kjs. 3, 7, 8, 9, and 18). In Fi(j. 3 of PI. I. they are represented from 

 above, so that the form of the space they circumscribe is best seen in such a view. 

 The circumscribed area consists, properly speaking, of two oldong, pear-shaped spaces, 

 tapering toward the central eye-speck, and widening forward and backward where 

 their outlines are rounded off. In Fig. 3 of PI. II. their termination near the eye- 

 speck is represented in a magnified view in the same position as in Fig. 3 of 

 PI. I. Fig. 9 of PI. II. represents one of these spaces in an oblique side view, 

 while Figs. 8 and 18 represent them in perfect profile from the side, so that their 

 height above the spherosome is plainly visible, the two halves being separated by 

 the eye-speck and its transparent cap. On the side of each of these spaces, about 

 mid-length but somewhat nearer to the eye-speck than to their rounded extremities, 

 may be seen on op230site sides the coeliac openings (PI. I. Fig. 3 ; PI. II. Fig. 9). 

 Fig. 7 represents in an oblique view the bulging of the bulb through Avhich these 

 apertures open. Nowhere among Ctenophora! are these coeliac openings more easily 

 seen than in Idyia, and nowhere is the circumscriljed area more distinct and more 

 jjromineut. I cannot, therefore, conceive how these animals can have been described 

 by earher observers as j^erforated in the centre, unless they were satisfied with 

 the most superficial inspection of very much injured specimens. 



Of all Ctenophorai the Beroids proper have the largest digestive cavity, and 

 in the genus Idyia it seems to have the widest dimensions, judging from the illus- 

 trations of the Beroe punctata and Forskali published by Eschscholtz and Milne- 

 Edwards. That cavity begins with a wide mouth occupying the whole length of 

 the actinal side, where the walls of the spherosome are thinnest, and extends very 

 nearly to the abactinal pole. Its outline, as seen from the Ijroad side of the body, 

 may fiiintly Ijc traced, especially on the actinal side, through the transparent sphero- 

 some, in PI. I. Figs. 2 and 7, and more distinctly in Fig. 10, PI. II., in which the 

 cavity is laid open ; while in Figs. 1 and 8 of PI. I. the anterior or posterior ambu- 

 lacra are so projected ujion it as to hide its outlines. In Figs. 3 and 4 its outlines 

 are faintly visible from the actinal and the abactinal side. In these si:)ecimens the 

 digestive cavity is gorged Avith chyme, so that the general outline of the body 

 is ovate, and the iuterambulacra are as turgescent as j^ossil^le ; but the figure is 

 not deformed by the presence of irregular pieces of food as in Fig. 10. In such 

 a condition it may be seen how uniform the thickness of the sjjherosome is in 

 every part of the body. In Fig. 10 the outline 'of the digestive cavity may also 

 be seen distinctly on the actinal side of that specimen, where it is contracted above 

 the mouth, and beyond which it closes over the larger Bolina wdiich fills it. It 

 thus appears, that while the digestive cavity is always wider in the direction of its 

 longitudinal diameter in consequence of its structure, its transverse diameter may 



