468 Prof. M'Intosli's Notes from the 



moreover, having the bluish tinge of the shell, which is also 

 somewhat elongate. An almost inexhaustible stock of young 

 mussels could thus be obtained at an early stage for trans- 

 porting to any fresh site. Their attachment, moreover, is 

 readily loosened (as in the older stages), for if the water in the 

 vessel be impure, they leave the zoophytes and congregate at 

 the margin of the water inside the vessel. 



Before they are found in these dense masses on the 

 zoophytes they often occur amongst the sandy debris around 

 the older mussels, and of course are very abundant in the 

 bay generally, as formerly mentioned *, indeed they constitute 

 one of the most striking features of collections of pelagic organ- 

 isms. While in May and June they are comparatively few, 

 they increase vastly in number in July and August, both at 

 the surface and towards the bottom. Moreover their size some- 

 what increases as the season progresses, especially towards the 

 bottom of the water, those in the upper parts preserving 

 pel haps greater uniformity in size throughout the season. 



The duration of the existence of these young mussels on 

 Gonotliyra'a and similar zoophytes is limited, for towards 

 the end of September only the stumps of the former are found 

 on the adult mussels, the rest having been swept away to 

 other sites. Numerous young mussels, however, still cling 

 to the stumps and to the rough surface of the adult shells. 

 They have now grown considerably — varying as a rule from 

 23" to y'y of an inch. Successive crops of Gonothyrcea thus 

 serve as a nidus for the attachment of the young mussels, 

 which thereafter seek new ground for further growth. 



It is many years since I pointed out the peculiar sites 

 sometimes chosen by the young mussels on quitting their 

 pelagic existence. Thus, previous to 1860 1 it was often 

 observed that they attached themselves to the sockets of the 

 eyes of Carcinus mcenas, and during growth caused evulsion 

 of the ocular peduncles and injury to sight, and so with 

 the antennules, while others fixed the abdomen of the crab 

 to the cephalotliorax by their byssi, so as to interfere with 

 reproduction. Some time ago mussels of considerable size 

 were found in more than one instance in perfect health on 

 the gills of the haddock %, their growth causing the oper- 

 culum to bulge outward and greatly to impede tlie functions 

 of the parts. It has often been shown that the Gadoids 

 in their young condition are very fond of feeding on the 



* ' Report of H.M. Trawling Cdiiimissioners,' &c. 

 t Thesis Uuiv. Edinb. pp. 18 and 19. 



X These specimens were lately in the Glasgow Exhibition, and are 

 now in the University Museum, St. Andrews. 



