228 The Irish Nahiralist. December, 



Alder had combined with Actaeonia in 1869. The develop- 

 ment of Actaeonia (Cenia) Cocksii appears to be unique 

 amongst opisthobranchs, since the species undergoes no 

 larval metamorphosis, the veliger stage being suppressed, 

 so that the animal leaves the egg in a form differing from 

 the adult in little more than size and the absence of tentacles 

 (see Pelseneer, loc. cit). 



Observations on Actaeonia were continued at the opening 

 of the present year with material from Bullock. Four 

 specimens were taken there on the 30th January. Two 

 of these were 6 mm. in length, the others about half that 

 size, the head-appendages being distinct but blunt and 

 short in the smaller specimens, long and tentacular in the 

 larger. After little more than three weeks the head- 

 appendages in the smaller specimens had grown so far as 

 to be indistinguishable from those of the larger. These four 

 individuals produced two egg -clusters. One, of only 2 eggs, 

 the smallest number I have seen laid by Actaeonia, was 

 deposited in the dish with the larger pair of specimens 

 on the 25th February, the second of 18 eggs was laid on 

 the 5th March in the dish with the originally smaller pair. 

 None of these eggs fully hatched out, though in the larger 

 cluster, development proceeded so far as to show the eye- 

 spots and traces of pigmentation in the embr3^os. 



On the 3rd March last, while examining some tufts of 

 Cladophora taken in half-tide pools at Bullock the day 

 before, I found adhering to a spra}^ an egg-cluster o Actae- 

 onia with 12 eggs, which, judging b}^ their state of develop- 

 ment, had been deposited about a week earlier, since the 

 embryos were already revolving within the egg -case. This 

 cluster of eggs hatched out successfully on the 19th March, 

 and the young Actaeonias lived and thrived in captivity 

 up to the following loth May, or for fully seven weeks. 

 I was' thus enabled to study the development not only within 

 the egg, but almost up to the adult stage. Little need be 

 said here of the early development or embryology of these 

 Actaeonias. It follow^ed closely the various stages so 

 lucidly described and figured in the paper already referred 

 to of Dr. Pelseneer, to w^hose kindness I am indebted for 

 a copy of the reprint. As Dr. Pelseneer's observations 



