Chap. II. 



AURELIA TLAVIDULA. 



49 



FUj. 1. 



Longitudinal sectional view of the Eye of Aurelia 

 FLAviDULA, corresponding to Fig. 11, PI. XI"!. ; designed 

 from nature by H. J. Clark. 



there is a single tentacle (1) and two tentacular lobes (^'^), one on each side; 

 in the distance are two smaller tentacles (2 and 2"), one contracted, and the other 

 extended, whose bases have a common wall (t) directly below the large single 

 tentacle just mentioned ; and finally there is a third tentacle (5), still further in 

 the distance and on the extreme left, whose walls unite, at the base (t), obliquely 

 upwards and laterally, with those of the longer tentacle (2") of the second row. 

 Beyond all these the lower margin (s) of the socket may be seen. The length of 

 the tentacles, when they are fully extended, is about one third of the radius of the 

 disk; they are quite slender and frequently coil upon themselves in spiral tresses. 



The next phase is the last of the series which we have studied connectedly. 

 At this age (PI. XI". Figs. 1, 2, 7, 8, 9, and 11; and Fig. 1) the diameter of 

 the disk is very nearly an inch and a half, 

 and there are fifty tentacles on each mar- 

 ginal segment. The essential addition to the 

 oi'ganization is the develojDinent of two tubu- 

 lar prolongations (PI. XP. Fig. 2 d^, Fig. 

 11 d^) of the radiating canals, in each ocu- 

 liferous lobe. These tubes are formed in 

 the same way as the canals from which 

 they arise, and are peculiar in shape ; 

 starting at an angle of forty-five degrees to the canal of the lobe, each one projects, 

 for one half of its length [a y), in a straight line, into the midst of the lappet, 

 and then bending (y) slightly inwards, proceeds as far again, and terminates. with 

 a closed end. Like the chymiferous canals, these blind tubes are embraced by 

 a single wall (c k), above and below. The exterior edge {Figs. 8 and 11 fi) is 

 rounded, but the inner one thins out. If we follow the walls ((,'«) backwards, 

 we trace them on one side into the inner wall {/P) of the ocular peduncle, and 

 on the other into the wall of the radiating canal (c). Like the latter, this is 

 transversely and finely wrinkled, and has a very delicate, filmy appearance. The 

 relations of the ocular peduncle to the surrounding walls are quite difficult to under- 

 stand, and therefore we have endeavored to make them clear by means of a highly 

 magnified drawing, Avhich shows this organ as seen from above (PI. XP. Fig. 11). 

 In order to make matters as distinct as j^wssible, we will refer at the same time to 

 the wood-cut above. Fig. 1, representing the same in profile and with a lettering 

 which corresponds with that of the illustration on the plate. First we have a bridge- 

 like portion (f) of the oculiferous lobe, which stretches across the base of the inter- 

 val between the lappets (f), and joins the latter at a short distance (dj) within their 

 inner margin, which it follows all around. Along the commisure [bj) of the lappets 

 the outhne of the bridge has the shape of a W (aj), and the wall is very thick; 



7 



VOL. IV. 



