50 DISCOPHOR^. Part III. 



but it thins out toward the free edge [j^). From the middle of the lower surface 

 of this bridge, the ocular peduncle {h^ h^ U W) is suspended, and as we see it from 

 above, we look directly into the base {li' It'), which here presents a circular outline. 

 On the exterior side {Iv'), the walls join those of the bridge quite abruptly, and on 

 the opposite side {h^), at a more oblique angle, though sufficient to produce a 

 strong outline ; but on the sides {h^), the passage is gradual, and with a long curve. 

 The outer wall {h^) is nearly as thick as one quarter of the diameter of the pedun- 

 cle, and thus it continues into the base, where it thins out into the outer wall of 

 the bridge. The inner wall (/r) is about half as thick as the outer one, and is 

 hollow to within a short distance of the facets {h*) ; passing inwardly to the base of 

 the peduncle, it gradually decreases in thickness, as it merges into the wall (e) of 

 the blind tubes {d^), in the lappets, and of the radiating canal (c*). The lappets (/') 

 of the oculiferous lobe appear to have a double commisiu'al mai'gin {bj cj), but the 

 true commisure [hj) is a little exterior to the W shaped margin of the bridge, and 

 what appears to be a second commisure {cj), is only the end of a sinus or short 

 furrow, which extends baseward, on the under side (see Fig. 1 hj cj). The eyes 

 ij(^) have increased greatly in numbei', and the reddish-brown pigment spot, which 

 is so conspicuous in the adult (PI. VI. Fig. 4) just below the facets, is quite dense. 



As we have already indicated, the radiating canals (PI. XP. Fig. 2 c c^ <?) pre- 

 sent a ragged outline, owing to the manner in which they are formed or extended 

 (PI. XP. Fig. 17 c^ c^), the uj)per and lower walls separating irregularly rather than 

 along a continuous line. The tentacles (PI. XP. Figs. 1 and 9 i^) are channelled 

 {Fig. 1, d d^) to the extreme apex, and communicate at the base {Fig. 9 ^i) with 

 the circular canal {mc). 



In the last phase we have shown how the young tentacles (PI. XI''. Fig. 13 2 

 and 2") arose side by side, without any intervening lobe ; and now we have to show 

 how they finally become sej)arated, and each is inclosed in a separate socket. The 

 outer wall, at the edge of the disk, simply protrudes, hernia-like {Fig. 9 c), between 

 the bases of the tentacles, forcing them apart, as it were, and gradually enlarges to 

 its full dimensions without any further changes. It is plain enough, from this, that 

 the develojiment of the tentacles is not strictly serial, right and left of the first one 

 that appears, but in a degree complicated; although the general progress is along 

 the edge of the disk toward the oculiferous lobes, so that after a while, the middle 

 of each segment supports a single row of tentacles, whilst further along, toward 

 the lobes, the series is less simple, varying from one to two, and finally three 

 rows. The walls of the tentacles are very transparent, and on this account furnish 

 great facilities for the study of their histological structure. The outer wall {Fig. 

 1 a to a^) varies considerably in thickness, not only on account of the degree of 

 extension or contraction, but on account of the thick beds or groups of lasso-cells 



