Section IV, 1918 1145] Trans. R.S.C. 



A Report on Cross Fertilization Experiments, 



(Asterias x Solaster) 

 Robert Chambers and Bessie Mossop 



Presented by J. P. McMurrich, Ph.D., F.R.S.C. 



(Read May Meeting, 1918) 



During the first two weeks of August, 1917, a number of adult 

 Solaster endeca (Forbes) were obtained by dredging over a rocky 

 reef in the vicinity of Joe's Point near the Biological Station, St. 

 Andrews, N.B. At this time mature Asterias forbesii (Desor) were 

 to be had at St. Andrews. The extent of the breeding season of 

 Asterias in the vicinity of St. Andrews may be estimated from the 

 occurrence of Bipinnaria in the plankton of Passamaquoddy Bay, 

 which is being investigated by Professor J. P. McMurrich. During 

 1916 the first Bipinnaria observed occurred on July 20th. They 

 were present in all subsequent tows till August 31st. In 1917, none 

 appeared till August 8th, after which date they appeared throughout 

 the remainder of the month. 



The Asteriidse and the Solasteridae are comparatively closely 

 related families, both belonging to the order Cryptozonia in the 

 Asteroidea. The Solaster possesses a heavily yolk-laden ovum ( 1 mm 

 or over in diameter) which undergoes a somewhat incomplete meta- 

 morphosis, the free swimming larva not having a completely formed 

 alimentary tract. The Asterias, on the other hand, undergoes com- 

 plete metamorphosis, the larval form being a typical Bipinnaria. 



Because of this and because of the fact that the spermatozoa of 

 the two species are very much alike, although the ova are very dis- 

 similar in size, the possibility suggested itself that interesting results 

 may arise from attempts at cross-fertilizing these two species. 



Among the specimens of Solaster procured, the females contained 

 large numbers of apparently mature ova. Repeated attempts at 

 fertilizing them with spermatozoa of their own species as well as with 

 those of Asterias proved unsuccessful. The breeding season of 

 Solaster, according to Gemmill,^ is normally in March or early 

 April, at least for those on the British Coast. This may account for 

 our failure with the Solaster eggs so late as July and August. On the 



1912, Gemmill, J. F., The Development of the Starfish, Solaster endeca, Forbes, 

 Transactions Zoological Society, London, Vol. 20, p. 1. 



