H 



TH. MORTENSEN, 



(Schwed. Siidpolar-Exp, 



PENTEr): no detailed description or figures being given by Andersson this could 

 not be decided by ClaRK. As will be evident from the description given here the 

 identity with Carpexter's Antedoii angustipinna is out of question, alone the dif- 

 ferences in the oral pinnules being so great as to decide the matter. It is much more 

 the question whether the species described here can really be retained in the genus 

 Isometra, one of the more important characters of the genus being that the oral pin- 

 nules are slender, styliform«, with elongate joints, which does not fit ver\' well with 

 the present species. Still, I prefer to leave it in the genus hoinctra in spite of this 

 and other minor discrepancies; the expanded joints of the genital pin- 

 nules being the main character of the genus. It is true, this widening 

 is much more developed than in the type species; but this would hardly 

 be a good reason for excluding this species from the genus, as it is 

 evidently a special adaptation for the care of the brood; and, in regard 

 to this question, it is decidedly more important that the male genital 

 pinnules are also expanded, and in a way corresponding very closely to 

 what obtains in the type species ( Challenger ^ Comatulidae, PI. XIII. 

 Figs. 5 a, b). 



The main interest with this species, of course, attaches to its care 

 of the brood and the special adaptations connected therewith. After 

 the careful description given by K. A. Andersson in the paper quoted 

 there is no reason to enter here again in a more detailed way on this 

 matter. I can in general confirm AndersSON's observations, as well 

 with regard to the way the brood is cared for, as with regard to the 

 remarkable fact that the central cavity of the ovary contains numerous 

 spermatozoa, which appear to enter through the wall of the ovary to- 

 wards the brooding chamber, not through a preformed opening. As 



Fig. 13. Genital 

 tentacle of Iso- 

 nietra vivipara^ 

 in ventral aspect, 

 showing the slit- 



like opening of K. A. ANDERSSON says, this would appear to necessitate a sort of copu- 



mar=upium. -^^^^^^ -^^ ^j^jg specles. The fertilization probably occurs within the ovary 



itself I have, however, not succeded in finding any fertilized eggs still 



lying within the ovary; on the other hand I have not observed any unfertilized eggs 



either within the brooding chamber. 



The shape of the brooding chamber may be seen from PI. II, Figs. 6 — 7 and 

 textfig. 13. The ventral side of the marsupium is formed by a thin, naked membrane, 

 with no calcareous deposits in it. The short, narrow, slitlike opening is situated close 

 to the ambulacral furrow. 



A detailed account of the embr)-onal development will be given in the memoir 

 under preparation, as mentioned in the introduction. I would here only state a few 

 facts concerninsT the later larval stages. 



