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



supplied about five times a week with fresh sea water brought 

 from some distance from the land. Under these circumstances 

 the larvae developed much more successfully, but there was com- 

 paratively little difference between those with the plunger and 

 those without. In some cases the plunger was absolutely harmful, 

 and the larvae in the vessels to which it was attached died off very 

 rapidly, but this was no doubt due to some impurity accidentally 

 present, for in other cases the larvae flourished as well with the 

 plunger as without it. 



The results obtained differed very greatly according to the 

 species ; Sphaerechinus granulans, and hybrids with this species, 

 never developed further than the stage reached about the 8th day; 

 although they sometimes lived as long as three weeks. Strongylo- 

 centrotus lividus and Echinus microtubercidatus, on the other hand, 

 and also the hybrids between these, continued to grow and 

 develop. In the first lot, tried in March and April, the cultures 

 were destroyed by using a dirty plunger when they had already 

 reached an advanced stage, but in May and June others were 

 started, in which many larvae survived until they became young 

 urchins, and those which grew most rapidly were simply supplied 

 with fresh water from a distance, without the use of a plunger or 

 of specially large jars. The Strongylocentrotus larvae began to 

 metamorphose after 34 days (May 14 to June 17), and the hybrids 

 from Echinus eggs by Strongylocentrotus sperm reared at the same 

 time produced urchins after 27 days. The Echinus larvae on this 

 occasion reached an advanced stage, and then gradually died off, 

 but another attempt yielded several young urchins after 32 days 

 (June 23 to July 25). The cross Strongylocentrotus female by 

 Echinus male is difficult to obtain, but on one occasion some 

 healthy plutei were produced, which at first grew more rapidly 

 than the converse cross, and afterwards died off. 



In the hot weather it is necessary to cool the jars with a slow 

 stream of running water, but no other precautions were taken, and 

 most of the larvae seemed to grow quite healthily. It appears 

 therefore that while with certain species very special precautions 

 are necessary in order to rear the more advanced stages, in others, 

 especially Strongylocentrotus lividus, these can be obtained in the 

 spring and early summer with no great difficulty if the larvae are 

 supplied with clean water containing food. 



A detailed account of the later plutei and young urchins is 

 outside the scope of this paper, since accurate accounts of their 

 external features have been given by Bury, Theel, and MacBride 

 in the papers referred to above, and no anatomical observations 

 were made in this case. The plutei resembled those figured by 

 MacBride very closely, and the young urchins were not very 

 different from those figured by Bury and Th6el. Some of the 



