108 MYTILIDJS. 



the glass. It is also curious to notice a young mussel 

 in a rock-pool, slowly and painfully warping itself along 

 by its extensile foot, the point of which is attached like 

 the sucker of a leech. The foot is stretched far beyond 

 the beak of the shell on the anterior side. For anato- 

 mical details of the animal I would refer my readers to 

 the admirable treatise of Professor Loven on the deve- 

 lopment of the Lamellibranchiate Acephala. The fry 

 has two very distinct eyes, which soon disappear and 

 are quite absent in the adult. The cilia which clothe 

 the gills are extremely beautiful and interesting objects 

 of microscopical examination. If a small portion of 

 one of the gills is cut off and put into sea-water, it will 

 swim about for a considerable time by means of these 

 cilia, appearing like an independent animal. The shell 

 sometimes grows to a colossal size. In the ' Transac- 

 tions ' of the Imperial University of Moscow for 1863 

 is a notice by Dr. Nordmann of a gigantic form of the 

 present species found by Holmberg on Edgecombe Isle 

 in Russian North America. One specimen, which is 

 figured of the natural size, measures upwards of 9 

 inches in length and 4} in breadth, and is stated to 

 weigh 1 Ib. 5 dr. 16 gr. The stunted variety (incurvata) 

 forms on some parts of our rocky coast a mass so closely 

 packed that the point of a knife could scarcely be thrust 

 between them. This was probably the " amazing bed 

 of small mussels " mentioned by Pennant in his ' Intro- 

 duction to Arctic Zoology/ and as to which he remarks, 

 " I think they were brought there by sea-fowl to eat at 

 leisure " ! Fabricius says it is viviparous, and that in 

 the spring he has found the fry lodged within the hinge 

 of their parent's shell ; but it seems more probable that 

 this was only a place of temporary shelter for them. 

 In the Shetland Isles the edible mussel is called " Crock- 



