ON THE DEVELOPMENT OF SOME BRITISH ECHINODERMS. 13 



not very ripe. To open the specimens and take out the eggs did not 

 prove good either for the same reason. However, some results were 

 obtained from the eggs got at the first experiment. The development 

 proved to be comparatively slow. The first indication of the postero- 

 lateral processes was found on the 30th, i.e. in ca. five days old embryos. 

 The embryos are remarkably elongate, and the oral lobe remains very 

 large after the formation of the said processes. On the 1st July I found 

 the first rudiments of the skeleton. On the 4th July there was seen the 

 first indication of the postoral rod, and the postero-lateral processes had 

 somewhat increased in length — but herewith the development apparently 

 ceased ; tlie larvae were alive and apparently healthy when I left on the 

 loth July, but the development was not advanced beyond the stage 

 reached on the 4th. Probably again the food was not suitable. 



The development reached a sufficiently advanced stage to show that 

 the body skeleton is simple, without recurrent rod. The cross-rods are 

 thorny. The body skeleton is upon the whole small, the rods short. 

 Unfortunately I can give no figure of it, the skeleton having been dis- 

 solved in all the preserved specimens as explained above. The colour is 

 yellow, or at the point of the postero-lateral processes, yellowish green : 

 there is no indication of red pigment. 



Though the rearing of this larva was thus not very successful, the 

 results obtained are not without value ; from the indications given here 

 it will doubtless be possible to recognize the Ofhiocoma larva, when it is 

 found in the plankton. The two Ophiurids, Oyhioihrix fragilis and 

 Ophiocoma nigra, are by far the most numerous Ophiurids occurring at 

 Plymouth ; they must almost cover the bottom on large areas. The 

 larvae of both forms must occur in large numbers in the full breeding 

 seasons of the two species. As the larva of Ophiothrix is well known, it 

 must be possible to find out, with the help of the indications given here, 

 which larva belongs to Opliiocoma, and in all probability the larva is 

 already known. In a paper on Loch Sween (" The Glasgow Naturalist," 

 Jnurn. Nat. Hist. Soc. of Glasgow, IV, 1912) Professor J. Graham Kerr 

 has figured (p. 43, Fig. 4) a very peculiar Ophiurid larva, which agrees 

 with the Ophiocoma larva in having a simple body skeleton and a very 

 large preoral lobe, it occurred in immense numbers at the beginning of 

 August — the season thus being likewise in accordance with the sugges- 

 tion that it is the Ophiocoma larva. In fact, Graham Kerr himself gives 

 that suggestion, and I think it very probable that he is right. The most 

 conspicuous peculiarity of this larva is the development of four " epau- 

 lettes," as I have previously found in a larva from the Bermudas de- 



