486 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



middle of March, 1913, I had no difficulty in obtaining 

 and fertilising an abundant supply of eggs; and, during 

 recent years, many workers at the Biological Station have 

 had the same success throughout April. It may be men- 

 tioned in passing that ripe adults may generally be 

 stimulated to emit the genital products from the gonads 

 by exposing the tank in which they are kept to direct 

 sunlight, or by adding some slightly warmed sea-water. 

 The fully developed echinopluteus stage of the larva of 

 Echinus esculentus may be at once recognised by its posses- 

 sion of two series of ciliated epaulettes (fig. 49, PL VIII, 

 a.c.ep. and p.c.ep.) which are charged with reddish-yellow 

 pigment. Even at an earlier stage, when the anterior 

 epaulettes only have developed (fig. 50), it may be dis- 

 tinguished from the larva of Echinus miliaris by its larger 

 size, more rounded form and comparatively longer arms. 

 Echinus (or P sammechinus) miliaris is a much less 

 abundant species in the neighbourhood of Port Erin than 

 Echinus esculentus. Its larva (fig. 51, PL VIII), on the 

 contrary, has occurred much more frequently in the 

 plankton, and was tolerably common in July, 1907, and 

 again in 1908. During the same month in the three 

 succeeding years, 1909-1911, I did not see a single speci- 

 men; but it reappeared in the plankton, along with the 

 ophioplutei with which it was associated in the earlier 

 years, in September, 1911, and again occurred in the 

 same month in 1912 and 1913. The echinopluteus of 

 Echinus miliaris is smaller than that of E. esculentus, and 

 its antero-posterior diameter is proportionately shorter. 

 The full-grown echinopluteus is, however, most easily 

 recognised by having only one series of ciliated epaulettes, 

 at the base of each of which is a rounded mass of green 

 pigment (fig. 51, gr.p.). Gravely and I collected a large 

 series of this larva, in which we were able to follow the 



