44 DISCOPHOR^. Pakt III. 



and, finally, the contents of the cell behind correspond to the vitreous humor {i]). 

 As if in confirmation of all this, we find that the focus of the lens corresponds 

 to the bottom (c) of the cell. What may be the office of the cylindrical cavity 

 (l) in the lens, we have no means of ascertaining; but it looks as if it might 

 be a means of correcting the spherical aberration; at least, it must afiect the 

 direction of the central rays more or less. Taking the lens by itself and without 

 any reference to the other parts of the organ, we have sufficient warrant, from 

 its form and position, in assuming that it is a true crystalline lens, and subserves 

 the jjurposes of actual vision. The eye of Cyanea has a similar structure ; and 

 such do we think must be the structure of the eyes of many, if not of all, the 

 covered-eyed Medusge. 



The Lasso-cells. The form of these cells (PI. XI.*" Fiff. 16") is oval, and their 

 length is about 35V0 of an inch.^ The straight, rod-like part {b d) of the thread 

 projects along the axis of the cell nearly to the opposite extreme, and then bends 

 abruptly upon itself {d), and, returning again nearly to its base, curves (<?) directly 

 across the cell and immediately commences its coil, at the same time closely 

 following the face of the cell-wall («). It makes in all only seven or eight trans- 

 verse, widely separate coils (/), and terminates (c) at the end opposite its base 

 {h). From this it will be seen that the rod-like base of the thread is not excentric, 

 as in Coryne, but is completely enveloped by the spiral coil. 



The principal features which mark the next stage (PL XP. Figs. 16, 17, and 

 26) are, the broadening of the marginal intervals {Fig. 26 «^), so that they are as 

 wide as the breadth of the oculiferous lobes (/) ; the appearance of two of the 

 marginal fringes {Fig. 16 a}) of the proboscidal jDrolongations, of Avhich we had 

 an intimation, in the previous stage (PI. XP. Fig. 4 a}), by the truncate corners of 

 the lips of the proboscis; and the incipient longitudinal folding of the proboscis 

 into four distinct lobes, so characteristic in the adult. 



After this stage, the breadth of the disk begins to increase rapidly, whilst the 

 oculiferous lobes are of comparatively slower growth. Of this we have the begin- 

 ning in the next phase (PI. XP. Figs. 25, 30, and 35); and this is the principal 

 feature which distinguishes it from the last. By the contracted state of one of 

 the ephyrae we were able to get a very good view of the transverse outline of 

 the radiating tubes [Fig. 30 c), and made out very clearly that the lower wall is 

 concave, and the upper one like the roof of a house, excepting that the two sides 

 are curved inwards. The cellular structure of the surface {Fig. 35) begins already 

 to resemble that of the adult; and here and there we find single lasso-cells (PI. 



^ The peculiar relations of the lasso-coil to the Prof. II. J. Clark. Compare my remarks on lasso- 

 rod-like portion of the thread were discovered by cells, in Proc. Amer. Assoc. 18-19, p. G8. 



