544 



TH. MORTENSEN : DEVELOPMENT OF 



of the family Toxopneustidœ. On the other hand, I maintained that 

 another common Japanese sea-urchin, Sphœrechinus pulckerrimus, is no 

 Sphœrechinus at all, but a true Strongylocentrotìis. — As regards the 

 position of the genus Strongylocentrotìis, I was somewhat in doubt, 

 thinking it most probably to form a subfamily of the Toxopneustidœ. 



These conclusions, arrived at mainly from a comparative study 

 of the pedicellariae of these forms, have not met with a complete 

 approval. While they were in the main accepted by Döderlein, another 

 authority on recent Echinoids, H. L. Clark, is for the main part 

 strongly opposed to them. — I shall, of course, not enter into details 

 here, the more so, since I have at present no access at all to the 

 necessary literature. — I was then naturally very anxious to study the 

 development of these three forms, in order to see if any deductions 

 could be made from the shape and structure of their larvae. 



While I have got the complete development of Toxocidaris 

 tubcrculatus and nearly so of Strongylocentrotìis pulcherrimus, I could 

 not obtain the development of Pseudocentrotus depressus, because its 

 sexual products were not ripe yet at the time I had to leave Japan. 

 But the first two, I am very satisfied to say, proved to be in ac- 

 cordance with my views. 



Strongylocentrotìis pulcherrimus. — The larva of this species is in 

 its younger stages very much alike to that of Strong, droebachiensis. 

 The body skeleton consists of a long club-shaped rod, the posterior 

 end of the body being thus elongated, as is the case in the larvae 

 of Strong, droebachiensis and of true Echinus species. This fact 

 induces me to think that, in reality, Strongylocentrotìis is nearly 

 related to the Echinidœ s. str. and not to the Toxopneustidœ, in which 

 latter family the larvae have quite another shape, viz. a short body 

 with a complicated body-skeleton forming a peculiar frame. So it is at 

 all events in Sphœrechinus gramdaris and — as I have been able to as- 

 certain here in Japan — also in Toxopneustes pileolus. I should be very 

 much surprised if the same does not prove to hold good for Pseudocen- 



