22 



of Asteroids and I lololhiirituis il soi'ins IkikIIv possiljlc lo ohliiiii ;iiti- 

 ficial ft'ililizalioii ol' I hose forms which liave large eggs, ricii in yolk. 

 Slill. 1 havi' iiu'l with Iwo siirpiising cxceplioiis lo this gciu'ral rule. 

 Ono of Ihc ohji'cls of my visit lo New Zealaiui was lo rear the larva of 

 Pscudcrhiims (ilbocinrliis (llullon): llic syslemalic posilion of this form 

 is vorv iiiici'rlaiii. and 1 expeiU'd l)y means of rearing its lai\a lo be 

 able to settle I he (juestion of its line affinities. Perfectly ripe specimens 

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

 way fertilization was never obtained. The small transparent eggs were 

 surrounded by the actively swimming spermatozoa, i)ut none of these 

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

 with an Echinoid of our own seas, namely Biissopsis lijiifera. It is pos- 

 sible that in lliis case the spermatozoa did entei' 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 haid to see. Possibly both species are 

 very sensitive to changes of tem|)crature, so that the failure may be 

 due to the temperature in the laboratory being somewhat higher than 

 in Iheii' natural surronndiiigs. 1 have, however, had no oppoilunity of 

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

 ceptional cases, so disa])])ointing from the view of the present researches, 

 arc very noteworthy and may give occasion to interesting experiments. 

 Although the total nundier of Kchinoids here studied is fairly con- 

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

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

 cially the Cidarids and Uiadematids. This is mainly dui' to the fact that 

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

 visit in the dilTerent 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 ()p])oi tunity of studying the develop- 

 ment of all the species occurring in such place. 



Eucidaris Thouarsi (Val.) 



I'l. V lMf>s. 1 2. 



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

 these already afTord more than usual interest, so that it seems jusliliable 

 to include a record of them heic. 



Ripe specimens were found in considerable numbers at Taboga. in 

 the Hay of Panama, in October 1\)\d, while in Xoxcmber and l)ecend)er 

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

 thus practically had ended before November. iVlthough artificial fertiliza- 



