Chap. VII. TIAROPSIS DIADEMATA. 309 



visible as far as the pigment spot {Fig. 14, e), but within the range of this field 

 they are so excessively transparent as to escape the powers of an ordinary micro- 

 scope. The inner wall {Fig. 12, b^) of the eye fills the Avhole length, breadth, and 

 depth of its thickness, and is a direct prolongation of the inner wall {h) of the disk ; 

 and as in the latter, its cells are too transparent to be seen with an ordinary objec- 

 tive. The optical apparatus proper consists of a row of highly refractive, globular 

 bodies (c), arranged in the form of a crescent, which lies parallel to the extreme 

 border («-) of the eye, and half way between the upper and lower surfiice, as we 

 may see by an end view {Fig. 15, c). Each lens of the coronet is enclosed by a 

 cell wall, in fact, it is the whole content of a cell. We have counted as many 

 as fourteen lenses {Fig. 12, c) in one coronet, of which the central ones are the 

 largest, and those on each side successively smaller. The circular tube (/) has 

 no communication whatever with the eye, nor with the pigment spot. 



The generative organs are represented on PI. XXXI. Figs. 9 and 9^ In the 

 region occupied by these organs, the radiating tube has the form of a deep oblong 

 pouch {Fig. 9, «'), which, when the edge of the disk is rolled inwardly, may be seen, 

 in a sectional view {Fig. 9"), to be broadest above («) and narrowed by one half 

 to a rounded bottom («'), in such proportions as to be one third deeper than the 

 greatest breadth. The innermost, or lining wall {Fig. 9, 9", b) of the disk, is 

 prolonged over the pouch, and becomes a thicker layer {b^) than in any other 

 part of the disk. Between this and the wall {a}) of the radiating tube, the eggs, 

 or spermatic particles, are developed. As the eggs increase in size, the outer 

 surfiice of the ovary becomes papillated by their prominence, and the color grad- 

 ually changes to a dark ))luish-grey. The chymiferous fluid circulates as freely 

 in the pouches as in the rest of the tubes, and rather more actively, and with 

 a greater variety of passing and repassing currents. 



Emhnjohgg. — On the 31st of March, 1855, we discovered the youngest Tiaropsis 



diademata Avhich we have ever had the good fortune to investigate. At that 



time the disk was deep bell-shaped (wood-cut 45), and about 



Fit], 45. 



one twelfth of an inch in diameter; the thickness of the pa- 

 rieties (5) nearly uniform, and, on the average, one fifth that 

 of the diameter of the bell, with a slight diminution toward 

 the lower edge {c), where it rounded oif abruptly; and the 

 aperture {ii) in the veil one third the marginal diameter of 



-a 



the disk. There were nine diversely developed tentacles 



Youngest Tiaropsis ob- •' ^ 



served, with forty tentacles, (wood-cut 46, « b (I) ou evcry quarter of the disk, making, 



and magnified disk. _ _ _ t • 



a opening iD the Teii.- 6 wall wlth tlic four primary ones {e), opposite the four radiatmg 



e e .-ci owere gauals, forty lu all. The four tentacles (a), intermediate to 



the four canals {g), were two thirds the length of the primary ones (e) and the 



