Mr Doncaster, On rearing the later stages of Echinoid Larvae. 47 



On rearing the later stages of Echinoid Larvae. By L. 

 Doncaster, B.A., King's College. 



[Read 24 November 1902.] 



In working at the development of Echinoids the chief diffi- 

 culty which all observers have met with has been in rearing the 

 larvae in the later stages, especially at the time immediately 

 preceding the metamorphosis. Echinoids have been reared from 

 the egg to the young urchin by Bury (Q. J. M. S., Vol. xxxviii. 

 1895), and Theel (Act. Soc. Reg. Upsala, 1892), and more recently 

 by MacBride (Journ. Mas. Biol. Ass. vi. 1, 1900), and Grave 

 (Science, Vol. xv. No. 378, 1902). Only the last two observers 

 succeeded in obtaining any considerable number of specimens 

 showing the later stages, and in both cases rather complicated 

 methods were adopted. MacBride reared his larvae in very large 

 jars, containing relatively few larvae, and fitted each vessel with 

 a "plunger," in order to keep the water perpetually in motion, 

 and further changed the water daily, and supplied the larvae with 

 fresh water brought from a considerable distance from land. 

 Grave succeeded in rearing the larvae without changing the 

 water, by supplying them with abundant food by means of a 

 species of diatom, but it is always possible that the particular 

 diatom may not be obtainable, and that the culture may thereby 

 be destroyed. 



When working this spring at Echinoid hybrids at Naples I 

 made efforts to rear the more advanced stages of the larvae, and to 

 obtain young urchins, with the object of comparing the hybrids 

 with the parent species. Attempts were made with Sphaer echinus 

 granulans, Strongylocentrotus lividus, and Echinus microtubercu- 

 latus, and with several hybrids between these species. The larvae 

 were kept in jars of four or five litres, covered to keep out dust, 

 and it was found that they lived healthily until about the 8th day 

 after fertilization when not supplied with fresh water or food of 

 any kind. After that time, however, they became less healthy, 

 ceased to develop further, and finally died off. 



In order therefore to rear the larvae further, special methods 

 were resorted to. Some larvae were put in an ordinary 4-litre jar, 

 and others in a similar jar fitted with a plunger, and both were 



