96 NOTES ON THE KEARING OF ECHIiNOID LAllVyE. 



siphoned off. It is advisable to have a small amount of a filamentous 

 alga, such as Edocarpus, floating in the water. Ulva, and other leaf- 

 like forms, are more apt to decay, and then foul the water. 



After the lapse of about eight to ten days, it will usually be seen that 

 in one or two of the jars, development is proceeding normally, whereas 

 in the others, symptoms of unhealthiness have appeared. The healthy 

 larvoo are then transferred to larger culture jars, in which they complete 

 the remainder of their development. The jars used for this purpose by 

 me had a capacity of ten gallons, and each was fitted with a large 

 plunger. Not more than 250 larvoe should be placed in each jar, and 

 as before, the water should be changed to the extent of one-third of its 

 bulk daily. 



It may seem to many that the course of proceedings which I have 

 sketched out is a very roundabout one. Why, it may be asked, should 

 not 250 blastuUe be transferred directly from the dish in which fertilisa- 

 tion is effected to the larger jar ? The answer is, that this course has 

 been tried and it failed. In a word, it is not possible for the experi- 

 menter to discriminate between larvae which have vigour enough to com- 

 plete their development and those which will soon die, until the second 

 week of their existence. We must, in the first instance, allow natural 

 selection to weed out the weaker. In this connection a curious fact 

 may be mentioned, A very successful result was obtained from a 

 culture of larva? proceeding from a fertilisation carried out very badly. 

 The eggs were piled on one another, several layers deep, and the water 

 remained full of spermatozoa all night. As a result, only about 10 per 

 cent, or less of the eggs became blastuloe. But those which survived 

 showed remarkable hardiness, and from them young echini were 

 obtained. 



Echinus esculentus and Echinus miliaris are decidedly different in 

 colour, size, and general appearance, and it is not therefore surprising 

 to learn that their larvre are different in every period of existence, as 

 has been detailed in a paper in the Quartcrhj Journal of Microscopical 

 Science (vol. xlii., 1899, p. 335). Here it need only be mentioned that 

 the larva of E. miliaris has only four ciliated epaulettes, and that the 

 young echinus at metamorphosis has one pair of tube feet in each inter- 

 radius, in addition to the azygous tentacle. The pluteus of E. esculentus 

 on the other hand has six ciliated epaulettes, which eventually coalesce 

 in order to form two circular bands of cilia, and the young echinus has 

 at first only the azygous tentacle in each interradius. 



The necessity for such frequent changes of sea-water seems to arise 

 rather from lack of food than from lack of oxygen, and it is more 

 urgent in some years than in others, according to variations in the 

 amount of vegetable plankton. In 1898 it did not seem so necessary. 



