REPORT ON THE ECHINOIDEA. 45 



the ovary, are passed along on the surface of the test towards the mouth, and the 

 smaller slightly spathulate primary spines, which are articulated to about the first three 

 rows of tubercles round the peristome, are bent inwards over the mouth, so as to form 

 a kind of open tent, in which the young are developed directly from the egg without 

 undergoing any metamorphosis, until they have attained a diameter of about 2 '5 mm. ; 

 they are then entirely covered with plates, and are provided with spines exceeding in 

 length the diameter of the test. Even before they have attained this size and develop- 

 ment, the more mature or more active of a brood may be seen straying away beyond the 

 limits of the ' nursery,' and creeping with the aid of their first few pau's of tentacular 

 feet out upon the long spines of their mother ; I have frequently watched them return 

 again after a short ramble into the ' marsupium.' " 



The specimen (PL II. fig. 2) shows the manner in which they are held in a sort of 

 marsupium by the folding of the abactinal spines over the young crowded upon the 

 abactiual system. This, as is shown in Plate II. fig. 7, cuts deeply into the median 

 ambulacral and interambulacural spaces. The female genital openhigs are notched in the 

 very edge of the genital plates. 



From among the many young collected by the Challenger, I was able to obtain two 

 most interesting stages of growth of this genus. Plate II. figs. 9, 10, represent from the 

 actinal and abactinal sides a young Goniocidaris, in which we find as yet no separation 

 of ambulacral or interambulacral plates. These areas are, however, most distinctly 

 marked by the presence of large primaiy tubercles and spines in the latter area, and by 

 the presence of three pairs of small tentacles in each ambulacral zone, surmounted by a 

 huge odd terminal tentacle (PI. II. figs. 9, 10, 18). The ambulacral tentacles are 

 separated by a vertical row of tubercles carrying small primary spines, but the test is 

 not subdivided into zones by plates ; it is as yet composed only of more or less close 

 reticulation and irregularly shaped plates, thickly covered with pigment spots. I 

 attempted in vain to find the eye at the base of this huge odd terminal tentacle, the 

 homologue of course of the odd terminal tentacle of the ray of the starfish, in which we 

 can so easily trace the eye in very early stages. The mass of pigment covering the 

 test, spines, and tentacles, made it impossible to observe the eye if it does exist. I 

 have also failed to see the eye in the young Echinids of other genera' which I had 

 occasion to examine, many of which were less advanced than the young of Goniocidaris 

 here described. This stage is interesting as showing perhaps more plainly than in any 

 other young Echinids I have seen, that the abactinal system is developed simultaneously 

 with the coronal plates from the primary reticulation of the test, whUe the actinal 

 system on the contrary is from the earliest stages separated as such from the coronal 

 plates. In a view from the actinal side (PL II. fig. 9) the ten buccal tentacles are weU 



1 See A. Agassiz, Jlem. Am. Acad., vol. ix, 1864, Embryology of Echinodenus ; and A. Agassiz, Kiubryoluj^y of the 

 Starfish, 1864, in Agassiz's Cont. Nat. Hist. U. S., voL v. ; also Menioii's Mus. Comp. Zool., vol. v.. No. 1, 1877. 



