218 



Appendices to Fourth Annual Report 



them ; yet the limpet forms a tough bait, which clings to the hook like a 

 button. 



Besides the special work just mentioned, many observations on the 

 phosphorescence of marine animals were made during the summer. These 

 formed the basis of the Address to the Biological Section of the British 

 Association * at Aberdeen. 



APPENDIX R— No. XIV. 



REPORT OX THE DEVELOPMEX'T OF THE COMMON MUS- 

 SEL, By John Wilson, Demonstrator of Zoology, University of 

 St Andrews. 



The literature of a strictly zoological character dealing with the common 

 mussel, as compared with that bearing on its relative the oyster, is scanty. 

 Especially is this the case in the field of embryology. To aflSrm that 

 the oyster has been the subject of much exhaustive study, one need only 

 refer to the superb memoirs on the development of the American oyster 

 by Mr Brooks,t and on the development of the European oyster by Drs 

 Hoek and Horst.J Such works are patterns worthy of imitation by those 

 who propose to conduct thorough investigations into the life-history of 

 moUusks, the multiplication and preservation of which it is of moment to 

 encourage. 



In 1856 Lacaze-Duthiers § gave an account of the development of the 

 gills of the common mussel, having studied forms one-fourth of a millimetre 

 in diameter. At this stage the gills appear, through the transparent valves 

 of the shell, as four separate, thickly-ciliated, club-shaped processes. In 

 the course of development those processes become more and more nume- 

 rous and coalesce, resulting in the familiar leaf-like gill of the adult. Of 

 the two lamellae constituting the fully-formed gill, the inner one precedes 

 the outer in development. In 1877 Sabatier j| published an elaborate 

 memoir on the anatomy of the adult mussel. The reproductive organs, 

 however, are but slightly touched on. Little attention seems to have 

 been given to the method and time of development of the generative 

 elements until 1884, when Professor M'Intosh, while conducting the 

 scientific investigations on behalf of Her Majesty's Trawling Commission, 

 studied these points. In the published account II of his observations 

 thereon he mentions the perfectly diuecious condition of the species, and 

 gives interesting details of experiments with spermatozoa, evidencing 

 their great tenacity of life after removal from the mussel. By examining 

 mussels at intervals from January to July, he found that in a sexually- 

 ripe, ' as compared with an undeveloped specimen, the mantle in J anuary 

 ^ is considerably thicker. A male, measuring 3 J inches in length, pre- 

 ' sented in the thickened generative region of the mantle large, pale, round, 

 ' sperm-sacs, filled with minute spermatozoa, which have ovoid bodies 

 ' with finely filamentous tails. The females had the same region of the 

 ' mantle crowded with a prodigious number of minute ova. As the month 



* Vide Eeport of the Association at Aberdeen, 1885, Section D (Biology). 



t Report of the Commissioners of Fisheries of Mar3'land, 1880. 



t Verslag Ocsterondcrzoekinge/i, Leiden, 1883-84. 



§ An. Sc. JVaL, ser. iv. tom. v. 



II An. Sc. Kat., ser. vi. tom. v. 



IT An. Nat. Hist., Feb. 1886. 



