22 



of Asteroids and Holothurians it seems hardly possible to obtain arti- 

 ficial fertilization of those forms which have large eggs, rich in yolk. 

 Still, I have met with two surprising exceptions to this general rule. 

 One of the objects of my visit to New Zealand was to rear the larva of 

 Pseudechinus albocinctus (Mutton); the systematic position of this form 

 is very uncertain, and I expected by means of rearing its larva to be 

 able to settle the question of its true affinities. Perfectly ripe specimens 

 were available, but in spite of several attempts carried out in the usual 

 way fertilization was never obtained. The small transparent eggs were 

 surrounded by the actively swimming spermatozoa, but none of these 

 succeeded in entering the eggs. Later on I have had the same experience 

 with an Echinoid of our own seas, namely Brissopsis lyrifera. It is pos- 

 sible that in this case the spermatozoa did enter the eggs, as a fertiliza- 

 tion membrane apparently began to form; but it never came to the 

 beginning of the cleavage. - The reason for the failure in obtaining 

 fertilization in these two cases is hard to see. Possibly both species are 

 very sensitive to changes of temperature, so that the failure may be 

 clue to the temperature in the laboratory being somewhat higher than 

 in their natural surroundings. I have, however, had no opportunity of 

 testing this suggestion by direct experiments. Anyhow, these two ex- 

 ceptional cases, so disappointing from the view of the present researches, 

 are very noteworthy and may give occasion to interesting experiments. 

 Although the total number of Echinoids here studied is fairly con- 

 siderable, the author is disappointed in being unable to give satisfactory 

 information about the larval forms within some important families, espe- 

 cially the Cidarids and Diadematids. This is mainly due to the fact that 

 the breeding season of these forms did not coincide with the time of my 

 visit in the different places; even under the uniform conditions of the 

 tropical seas they do not breed continuously, and accordingly a stay of 

 two-three months will not give the opportunity of studying the develop- 

 ment of all the species occurring in such place. 



Eucidaris Thouarsi (Val.) 



PI. V Figs. 12. 



Of this species only the very youngest larval stages were reared, but 

 these already afford more than usual interest, so that it seems justifiable 

 to include a record of them here. 



Ripe specimens were found in considerable numbers at Taboga, in 

 the Bay of Panama, in October 1915, while in November and December 

 only very few specimens had ripe sexual products; the breeding season 

 thus practically had ended before November. Although artificial fertiliza- 



