440 Prof. E. W. MacBride. Some Points in the [May 6, 



•obtainable after the treatment of the blood films with absolute alcohol, we 

 conclude that it is allied to that known as fatty. 



In conclusion, we desire to express our thanks to Dr. G. Buckmaster, and 

 to Dr. J. B. Leathes, for criticism and help in regard to certain of the points 

 raised by the investigation. 



Some Points in the Development of Ophiothrix fragilis. 



By E. W. MacBride, D.Sc, F.R.S., Strathcona Professor of Zoology in McGill 



University, Montreal. 



(Received May 6,— Read June 13, 1907.) 



The subject of which the present communication is a brief preliminary 

 account has occupied my attention during the last five years, and a full 

 account will be published shortly. Meanwhile, a brief outline of the main 

 results is given here. 



Ophiothrix fragilis is one of the commonest species of British Ophiuroidea. 

 Especially in the neighbourhood of Plymouth, where the material for this 

 research was obtained, this species is found in immense swarms, so that, on 

 certain kinds of bottom, hundreds of individuals are brought up with each 

 haul of the dredge. During the months of June and July it spawns, and on 

 some occasions the Plankton captured above the beds of gravelly sand on 

 which it lives is full of its larvae in all stages of development. 



A large quantity of this Plankton, captured during July, 1899, formed the 

 principal part of the material, but this was supplemented by artificial 

 fertilisation carried out in the laboratory of the Marine Biological Association 

 in the years 1898, 1899, and 1905. 



The eggs are small (about O'l mm. in diameter) and opaque owing to the 

 possession of a reddish-brown yolk. The development was observed to be 

 completed in 28 days, but the rate of development depends on the amount of 

 food supply in the water, and it is probable that in the sea the eggs 

 develop more quickly than under the most favourable circumstances in the 

 laboratory. 



Only on one occasion (June, 1898) was it found possible to rear the larvae 

 through their development until metamorphosis was completed ; this was 

 ■due to the presence of an unusual amount of Phytoplankton in the water 



