ECHINODEEMA. 



II.-EOHINODEEM LAEV^. 



By E. W. MacBride, M.A., D.Sc, F.R.S., Professor of Zoology, McGill University; and 

 J. C. Simpson, B.Sc, Demonstrator of Zoology, McGill University. 



(1 Plate.) 



The collection of larval Echinoderms brought back by the National Antarctic Expedition, 

 when received by us from the authorities of the British Museum, was found to consist 

 of forty tubes of material collected during the years 1902-1904. Of these forty tubes, 

 however, by far the greater number contain nothing but early segmenting eggs showing 

 no distinctive features ; the present paper is, therefore, in reality based upon the 

 contents of eight tubes only. 



A preliminary examination showed that, though the collection contained but 

 four species of Echinoderms, these differ widely from one another, there being one 

 representative of each of the four great classes of the sub-phylum Eleutherozoa. These 

 four species are : Asterias brandti Bell, Cucumaria crocea Lesson, a new Echino- 

 pluteus, and an Ophiopluteus which may also be new. 



At first sight the Asterias seemed to promise much, for there were two tubes 

 containing a couple of hundred specimens which had been born after the capture of the 

 mother. More careful examination, however, disclosed the fact that they were all 

 of approximately the same age, only two closely related developmental stages being 

 represented. In the case of the Cucumaria, besides a number of new-born young, the 

 collection contained an adult female which was the mother of some of them. To this 

 specimen considerable interest attaches, from the fact that in it an unsuspected brood- 

 pouch containing a great number of embryos was found. Of the two plutei it need only 

 be said in this place that, since they are probably the first free-swimming Echinoderm 

 larvae found within the Antarctic Circle, they are not without considerable importance. 



In the matter of preservation the material leaves much to be desired ; but when 

 one considers the difficulties of collecting under Antarctic conditions, it could hardly be 

 expected that this could be otherwise. Of necessity the only preservatives used were 

 formalin and spirit, and as neither of these is at all suitable to Echinoderm larvae, the 

 specimens show very little histological detail. 



In examining the material it was found that the preservation of the plutei was 

 such as to make sectioning useless, so they were studied in toto, first unstained, and 

 then stained in eosin and mounted in balsam. This method was found to give very 

 satisfactory results. The Asterias and Cucumaria, however, were treated quite 

 differently. Selected specimens of these were first carefully drawn at a magnification 



