94 Papers from the Marine Biological Laboratory at Tortugas. 



tendency of zoologists to ignore such evidence as there is. Recent work by 

 the Sollases (1912) is an encouraging step along the right lines. 



Finally, no attention whatever has been paid to localized stages, the 

 importance of which, in both plants and animals, was pointed out by 

 Jackson (1899) some years ago. They are remarkably well shown in the 

 ophiuran arm, and the attempt is made in the present paper to point out 

 some of them; the chief difficulty is our lack of knowledge, save in a very 

 few species, of the ontogenetic stages with which to compare them. 



Brittle-stars are conspicuously common on the reefs and shores of 

 Jamaica, and when I was invited to make use of the marine laboratory of 

 the Carnegie Institution of Washington, located, during February and 

 March 1912, at Montego Bay, Jamaica, I very gladly availed myself of 

 the opportunity, determined to secure, if possible, material which would 

 throw light on the post-larval development of some brittle-star. 



I wish to express here my thanks to the authorities of the Museum of 

 Comparative Zoology for the necessary leave of absence from my duties 

 there. 



Material was easily secured at Montego Bay and young stages were 

 obtained of three different brittle-stars. The purpose of the present paper 

 is to report the results of my studies on these three species, to sum up our 

 present knowledge of the post-larval development of brittle-stars, and to 

 suggest a few conclusions that may be drawn from this knowledge which 

 will be of service in future work. 



MATERIAL. 



Although species of Ophioderma and of Ophiocoma are the most common 

 brittle-stars at Montego Bay, no really youthful stages of species of these 

 genera were found. As Ophiocoma is known to breed in the early summer, 

 and Ophioderma is also a summer breeder, at least farther north, it is quite 

 probable that the season of the year was the reason why the young of these 

 genera were not found. This was to be regretted, since these genera repre- 

 sent widely different families and in neither is there any species whose 

 development is known beyond the metamorphosis. Grave (1900) has 

 worked out the early development of Ophioderma brevispina from material 

 collected near Woods Hole, Massachusetts, and has published a preliminary 

 account (1898) of the early stages in Ophiocoma echinata. In neither case, 

 however, were post-larval stages available, and I had therefore hoped it 

 might be possible to supplement Grave's work from material obtained at 

 Montego Bay. Although disappointed in this respect, I had the good 

 fortune to find that in the seaweed and fixed animal life (sponges, hydroids, 

 ascidians, etc.) which form great masses on the mangrove roots, at the 

 Bogue Islands, west of Montego Bay, brittle-stars literally swarmed. Of 

 these the commonest was Ophiactis savignyi (Miiller and Troschel), which 

 was exceedingly abundant in the cavities of a red sponge, individuals of 

 all sizes, from young with disk barely a millimeter across up to adults 



