182 



shaped, sometimes, however, they are more or less irregular, the vibratile 

 band forming lobes, as in the specimen figured in PI. XXXII, Fig. 7. 



The interior organisation of the larva is quite typical, though, as might 

 be expected, the digestive organs are to some degree rudimentary, in ac- 

 cordance with the fact that the larva has no opportunity of feeding on 

 other organisms, as do the free pelagic larvae. The esophagus is somewhat 

 less developed than in the typical larvse, and especially the mouth opening 

 is smaller, sometimes irregular in outline. The stomach is large and of 

 the typical shape; the rectum is sometimes quite unusually large, but 

 apparently there is no anal opening (PI. XXXII, Fig. 6). A more or less 

 distinct Hne of nuclei in the oral area (PI. XXXII, Fig. 3) would appear 

 to represent the larval nervous system. 



The enterocoel and hydrocoel vesicles are large and very distinct, the 

 hydrocoel having at first only 5 lobes; the sixth appears to form between 

 the 2nd and 3rd primary lobes. On metamorphosis the hydrocoel grows 

 upwards over the esophagus. In some cases there is a distinct right 

 anterior vesicle (PL XXX II, Fig. 1); in two cases a normally lobed 

 right hydrocoel was found, no trace of a left hydrocoel being 

 observable (PI. XXXII, Fig. 4). There is not the slightest reason to 

 doubt that these "righf'-specimens would have developed normally. This 

 case is quite unique in Echinoderm embryology. Larvae with both a right 

 and a left hydrocoel have been observed repeatedly, rarely in the free, but 

 not so rarely in cultures, and, as shown by MacBride^) can be produced 

 artificially; but, so far as I know, larvae with a right hydrocoel alone have 

 never before been observed, in nature or in artificial cultures. The theo- 

 retical interest connected with this case is very considerable. This is, how- 

 ever, not the place to enter on a discussion of this matter. 



Regarding the structure of the young Ophiurid I would only call atten- 

 tion to the fact that there is not one prominent central plate as is usually 

 the fact in young Ophiurids, but two or three of somewhat irregular shape 

 (PI. XXXII, Fig. 8). Mostly the young Ophiurids have the oral tentacles 

 very much extended (— the specimen figured is exceptional in this regard, 

 having the oral tentacles for the greater part retracted — ); they are 

 further conspicuous by the granulated appearance of their point. The sug- 

 gestion hes near that these tentacles may perhaps have some kind of 

 absorbing function. In any case it is clear that the food contained in the 

 substance of the small egg can by no means account for the large size 

 attained by the young within the brood sac. Nourishment from the parent 



') E. W. Mac Bride. The artificial production of Ecliinoderin Larva with two water- 

 vascular systems, and also of Larvse devoid of a water-vascular system. Proc R Soc B 

 Vol. 90. 1918. p. 323—48. Pis. 4—10. • . . u. 



