THE ANATOMY OF ALCYONIUM DIGITATUM. 351 



The matter seems to me to be worthy of further investiga- 

 tion, and it is to be hoped that some one who is able to remain 

 at the Plymouth laboratory for some months will repeat the 

 experiments. 



The sexual reproduction of Alcyonium digitatum occurs 

 on our southern coasts during the months of December and 

 January. The colonies are invariably dioecious. Although I 

 have opened several hundred colonies, I have never found a 

 single instance of ova and spermatozoa occurring together. 



Early in March the gonads may be seen as minute swellings 

 on the ventral and lateral mesenteries. These gradually get 

 larger and larger as the year progresses, but it is not until 

 August or September that any difference can be seen between 

 the ova and the sperm-sacs. The ova then acquire a pale 

 yellow tinge, which becomes redder and redder as the winter 

 approaches. The gonads do not reach their full size until 

 December. 



The spawning takes place in an aquarium very slowly, the 

 ova being shot out of the mouth, one by one, at considerable 

 intervals, and it may occur either by night or during the day- 

 time. Whether this is also the case in the natural conditions 

 I am, of course, unable to say; but colonies may be found at 

 the end of December in all conditions between those densely 

 packed with ova or sperm-sacs and those completely shotteu. 



Early in January the number of pregnant colonies becomes 

 smaller and smaller, until in the last week of that month 

 scarcely a single ovum can be found. 



The extraordinary long period (nine months) that elapses 

 from the first appearance of the gonads to the time they reach 

 maturity is particularly noteworthy. I can offer no satisfac- 

 tory explanation of it. 



I may say that there are no external indications of the sex 

 of a colony of Alcyonium. In shape, size, and colour the male 

 and female are the same. Nor is there any probability that, 

 as in some Hydrozoa, they are protandrous or protogynous, 

 for small colonies not more than an inch in height may be 

 either males or females. 



