48 



longing to this same larva I have shown in my "Echinodermen-Larven 

 d. Plankton-Expedition" (p. 91) that he made a mistake. These larvae, 

 which were caught free swimming, evidently belong to a Clypeastroid, 

 most probably Echinarachnius parma 1 ). But the main thing is that they 

 are not Sir. drobachiensis, and his statement of the presence of vibratile 

 epaulets in the Stronyylocentrolus-larva thus lacks real foundation. 

 Hereby I do not mean to ascertain that there are no epaulets in the 

 Str. drebachiensis-larva. On the contrary, 1 may take the opportunity 

 here to state that the Str. drobachiensis-larva has not only the usual 

 epaulets, but it has also a posterior pair of large epaulets, much as 

 in the larva of Echinus esculentus. This statement rests, not upon the 

 rearing of this larva, of which I have not as yet found an opportunity, 

 but on the evidence of a pair of specimens found in a plankton-sample 

 from Greenland, taken by Mr. K. Stephen sen in Bredefjord, South 

 Greenland, in the summer of 1912. As Str. drobachiensis is the only lit- 

 toral Echinoid of Greenland there can be no doubt that the larva belongs 

 to this species. Unfortunately the specimens are in a rather poor state 

 of preservation, so that they are not fit for being figured; but the epaul- 

 ets are distinct enough. It is a pity that the larva of Str. pulcher- 

 rimus could not be reared to metamorphosis so that the question whether 

 it has epaulets like drobachiensis could be decided. But in view of the 

 complete accordance with the drobachiensis larva in the earlier stages 

 there is every reason to expect that it will also prove to have epaulets 

 in the same way as that larva. 



Strongylocentrotus franciscanus (A. Ag.). 



PI. IX Figs. 14. 



The development of this species I had the opportunity of studying 

 while staying at the Biological Station at Nanaimo, Vancouver Isl., 

 B. C., in May June 1915. Fertilization was made on May 26th. The 

 eggs are small and transparent. 1 noticed the peculiarity that there is 

 found a double fertilization membrane, the outer one standing far out 

 from the egg, while the inner membrane remains close to the surface 

 of the egg and follows the outline of the cleavage cells, as shown in the 



M In the work quoted I have suggested that they might perhaps belong to Mellita textu- 

 dinala, pointing, however, also to their likeness to the Echinarachniu.i-\aTva. Mac Bride 

 in his Memoir on the Development of Echinus exculenlim (Philos. Transact. B. Vol. 195. 1903. 

 p. 287) still states that by this work of Agassiz "for the first time a complete history of 

 the changes in external form undergone in a single species was obtained". Evidently Mac 

 Bride must have overlooked my criticism of Agassiz' work. The honour of having for the 

 first time given the complete history of the development of an Echinoid (regarding the ex- 

 ternal form) belongs to Th6el (Echinocyamus), not to Agassiz. 



