Z DR. TH, MORTENSEN. 



classification of the full-grown animals. The embryological development 

 in itself is not at present the object of my researches, and in the present 

 report, therefore, only occasionally pure embryological facts are given. 



As I had, of course, not much time to study the living larvae more 

 closely, having so many different cultures going on at the same time, I 

 preserved material of the different developmental stages for study later 

 on. On examining the preserved larvae after my return to Copenhagen 

 I found that a very regrettable mishap had occurred. The alcohol in 

 which the larvae were kept had in some way or other become acid, and 

 the skeleton of all the larvae had been dissolved. As the specific char- 

 acters are especially found in the skeleton in those larvae which are pro- 

 vided with such, the value of my material had thus been considerably 

 diminished. Fortunately I had made a preparation in Canada balsam 

 of the larva of Ophiactis Balli while still in Plymouth, so that in this case 

 nothing was lost. 



After I left the laboratory my cultures were looked after for some time 

 by the attendant, Mr. Smith, and some of the later stages were sent me. 

 In this way I got the later stage of the Luidia larva ; a few larvae of S^pat- 

 angus purpureus, with the skeleton preserved, also came to hand, but in 

 so poor condition that only little use could be made of them. Of the 

 other larvae only a few of A. glacialis were obtained, but these were not 

 in a more advanced stage than that reached before I left the laboratory. 



I.— Asterias glacialis. 



The development of this species has never been satisfactorily worked 

 out, in spite of the fact that it is one of the objects commonly used in 

 experimental embryology. A. Russo, in his paper " Contribuzione air 

 embriologia degli Echinodermi e sviluppo dell' Asterias glacialis 0. F. 

 Miiller,"* describes the first developmental stages, until the formation 

 of the vibratile chord. Having reached this stage the larvae began to 

 degenerate. Some later stages, which were caught pelagically, were 

 also referred by Russo to this species (his figures 22-25) ; it is, however, 

 evident enough that they cannot belong to this species — the strong 

 development of the vibratile chord at the anterior end of the frontal (or 

 preoral) area, where the brachiolarian processes appear later on in the 

 Asterias larva, is sufficient proof that they cannot belong to an Asterias. 

 In my Ecliinodermenlarven der Plankton Expedition (p. 30), I have 

 given the name Bipinnaria Russoi to this larva. The rearing of the more 

 advanced stages of the A. glacialis larva has given the definite proof that 



* Boll. d. Soc. di Naluralisti in Na.f.oli, Ser. 1, Vol. \U (1892). 



