OPHIURA BREVISPINA. 



By W. K. BROOKS aiid CASWBLL GRAVE. 



INTRODUCTION. 



During the summer of 1808 it was my privilege to occupy the table of the Johns Hopkins 

 University in the United States Fish Commission laboratory at Woods Hole, and while here I 

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



Finding the lame he described in the open sea KROHN did not know to what species they 

 belonged; but the larva 1 , the development of which is the subject of the greater part of this paper, 

 came from eggs laid in aquaria by Ophinra brerispiua. It is not likely that the same species 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 Ecliinoderms, where a direct development from the larva to adult occurs, that is, 

 without the usual highly specialized intermediate pelagic larva, we usually have to do witli a 

 species which in some manner takes care of its brood; but in O. breoispina the larva; are free 

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

 pluteus larva is as completely omitted as it is from the life history of the viviparous Amphlura 

 squamata. 



From the fact that the usual pluteus skeleton is begun in the larvse of 0. brevispina 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 the larva} of 0. brevispina and Antedon rosacea (treated of in another place) we may 

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

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

 Echinoderm stock, then in the larva of 0. brevispina we may have one which has retained 

 unmodified its primitive characteristics. 



In this paper, however, the facts only of development are taken up, and the question of the 

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

 of the Ecliinoderms is suggested here in order that the reader may keep the subject before him 

 while studying the paper. The points of resemblance between the Ophiuran and Antedon larvre 

 are enumerated in a chapter further on. 



The method used in the preparation of the material for microscopical study, and which gave 

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

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

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

 solution was drawn off gently, leaving the larv;v at the bottom where they had settled. Then 50 

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

 alcohol, in which a little iodine had been dissolved. In a few hours (3-12) this was changed for 

 clear 75 per cent 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 modifica- 

 tion of the PATTON method. After an impregnation with 55 paraffin, series of sections three 



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