ON THE DEVELOPMENT OF SOME BRITISH ECHINODERMS. 11 



female is red, that of the male brownish ; the rays of the female are 

 somewhat broader than in the male, and upon the whole the male scarcely 

 reaches so considerable a size as the female. It is mostly quite easy 

 to distinguish between the sexes at a glance — quite apart from the fact 

 that generally the arms break so as to expose some of the gonads. 



In the stomach of this species I have found remnants of Ophiurids 

 {Ofhiotlirix). 



III.— Ophiactis Balli. 



On the 17th June several specimens of this species were taken on the 

 Eddy stone grounds, especially on tubes of Chcetopterus and on Ascidians. 

 Some of these were found to contain ripe sexual products ; they were 

 placed in a large jar with only a few centimetres of water, in order to try 

 if they would shed their eggs and sperm. Already next day I had the 

 pleasure of finding the fertilized eggs, which had partly already reached 

 the blastula stage ; at 12 o'clock, viz. after scarcely more than eighteen 

 hours, the first swimming blastulae were observed. On the 19th the 

 •embryos were found swimming actively close to the surface of the water ; 

 they were somewhat elongated, a little transparent at one end. On the 

 20th the first rudiments of the skeleton were formed, and the postero- 

 lateral processes had begun to appear, showing already an indication of 

 red colour at the point. On the 21st the larvse had already distinctly 

 the shape of an Ophiopluteus ; the antero-lateral and the postoral rods 

 (and processes) had begun to grow out, and likewise the recurrent rod 

 had begun to appear. On the 26th the body skeleton was completely 

 formed, and the three pairs of processes had become somewhat longer, 

 especially the postero-lateral. These latter processes are distinctly red 

 at the point ; also the postoral transverse chord has a reddish tint, the 

 larva being otherwise uncoloured. It always swims near the surface, 

 but at this stage does not any longer rotate round its longitudinal axis. 



Having reached this stage the development ceased ; the larvse still 

 Temained alive for some days, but without showing further advance. 

 Probably the diatoms were not suitable food for them. However, the 

 stage reached is sufficiently advanced for showing the characters of the 

 larva, so that it will be possible to recognize it also in later stages, the 

 •essential characters of the Ophioplutei lying in the body-skeleton, which 

 had, fortunately, already reached its full development (Fig. 13). 



The main features of it are the following : Recurrent rods are present, 

 whereby two large meshes are formed in each half of the body. The 

 cross-rods are peculiar in being slightly lobed at the end, the lobes of the 

 two rods of each side catching into each other. The end-rods are rather 



