OPHIURA BREVISPINA. 



By W. K. Brooks and Caswell Grave. 



INTRODUCTION. 



During the smniner of ISOS it was my i)rivilege to occupy tbe table of tlie Jolins TTopkins 

 University in the rnitetl States Fish Couunission laboratory at Woods Hole, and wliije here 1 

 rediscovered the peculiar Ophiuran larva, which was first found and figured by Krohn (7). 



Finding tbe larva- he des('ribed in the open sea Kkohn did not know to what species they 

 belonged ; but the larva', the development of which is the subject of the greater part of this i)aper, 

 came from eggs laid in a<iuaria by Ophinra hrcvispina. It is not likely that tlie same s])ecies of 

 Ophiuran occurs both at Funchal, where Krohn did his work, and also at North Falmouth, where 

 my material was obtained, but it is very probable that species belonging to the genus Ophiura 

 have similar larval forms. 



Among Ecliinodcrms, where a direct development from the larva to adult occurs, that is, 

 without the usual highly specialized intermediate ])elagic larva, we usually have to do with a 

 species which in some manner takes care of its brood; but in (>. hnrispliia the larv:c are free 

 swimming, they being provided with a well developed locomotor apparatus, yet the usual Ophiurid 

 l)luteus larva is as completely omitted as it is from the life history of the viviparous Amphinrn 

 squamata. 



From the fact that the usual pluteus skeleton is begun in the larva; of O. hrevispina one is led 

 to suspect, however, that at some period in its history the species possessed a larva more nearly 

 like a pluteus than at the present time. On the other hand, on account of the resemblances which 

 exist between tbe larva- of <). brevispinn and Antcdon rosacea (treated of in another ])lace) we may 

 suppose a close phylogeuetic relationship exists between them. If, as many zoologists believe, 

 the criuoids have retained more nearly than any other group the characters of the primitive 

 Echinoderm stock, tlien in the larva of O. hrtvispina we may have one which has retained 

 unmodifled its primitive charac-teristics. 



In this paper, however, the facts only of develoi)ment are taken up, and the question of the 

 bearing which this larva may have on any theoretical discussion concerning the interrelationships 

 of the Echinoderms is suggested here in order that the reader may ke(-p the subject before him 

 while studying the pai)er. The points of resemblance between the Ophiuran and Antcdon larva- 

 are enumerated in a chapter further on. 



The method used in tlie i)r(-i)aration of the material for microscopical study, and which gave 

 good results, is as follows: The larva- were taken up into a pipet with as little water as possible, 

 and squirted into a small bottle coutaiuing a solution of sublimate-acetic (98 parts of a sat. sol. 

 HgCl, being used to 2 parts of glacial acetic, acid). After from two to five minutes the sublimate 

 solutiou was drawn off gently, leaving the larva- at the bottom where they had settled. Then 5<t 

 per cent alcohol was added, which in a few miiuites (5) was drawn off and replaced by 70 per cent 

 alcohol, in which a little iodine had been dissolved. In a few hours (M-l'J) this was changed for 

 clear 75 per ct-nt alcohol, in which the larva- remained until needed for laboratory study. After 

 staining lightly in acid carmine, so as to facilitate their orientation, the larva- were dehydrated in 

 the usual way and cleared in oil of cloves. From the clove oil they were oriented by a moditica- 

 tiou of the rAXXON method. After au impregnation with 55° paralliu, series of sections three 



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