St. Andrews Marine Laboratory. 467 



2. Oil the Development o/'Mytilus edulis. 



In the ' Annals ' for February 1885 a few remarks on the 

 reproduction of the common mussel were noted. Amongst 

 other things it was shown that the development of the repro- 

 ductive elements of well-grown mussels from the Eden 

 had made considerable progress in January and February, so 

 that ripe sperms and well-developed ova were present. In 

 full maturity, as in April, the orange mantle further was 

 richly arborescent from the racemose sperm-sacs and ducts, 

 but less distinctly so in the female. The sexual elements 

 diminished in May, June, and July, the general stroma of 

 tlie mantle being vesicular and granular, so that the characters 

 of the sexes were absent. It was thus apparent that there 

 was a period of resolution aud rest as well as a period of 

 functional activity in the reproductive organs. The ova again 

 appear in the larger forms in September. 



Since that period the development of the mussel has been 

 the subject of a special research by Mr. John Wilson, B.Sc, 

 who has published several papers — the last illustrated by 

 three plates (4to) *. He found artificial impregnation of the 

 ova — by tearing the mantle carefully to pieces — the best mode 

 of procedure, and he was thus enabled to follow the early 

 stages, that are not so readily procured in the sea as the 

 later, in which the shell has attained considerable dimensions. 

 As had formerly been pointed outf, he also found that com- 

 paratively small specimens were mature, and that many of 

 those amongst the tidal rocks and elsewhere carried such re- 

 productive elements till August ; indeed, he partially suc- 

 ceeded in fertilizing ova on the first of the latter month. 



The main point of the present note, however, is the fact 

 that the older mussels in one part of the estuary of the Eden 

 are covered with dense feathery masses of Gonothyrcea^ upon 

 which the young mussels settle as soon as they quit pelagic 

 life, and thus an interesting phase in their history is deter- 

 mined. For many years it had been one of the ordinary 

 features of the district to find very young mussels on zoophytes 

 and seaweeds, especially on Ohelia and Oonothyrcea. By 

 watching the latter in the bed of the Eden and in the line of 

 the pelagic young it was observed that the mollusks first 

 settled on the zoophytes in July, the twigs being densely 

 covered with young mussels varying from yV to ^V of an inch, 

 some showing three gill-papillse, others thirteen, the larger, 



* Fifth Ann. Eeport, Fishery Board for Scotland. This important 

 paper has been overlooked by some recent writers on the subject, 

 t Ann. & Mag. Nat. Hist., Feb. 1885. 



33* 



