NATURAL HISTORY OF THE MUSSEL 51 



the middle of June, before a deposit of minute 

 mussels is observ^ed.' 



A detailed description of the embryo mussels, in 

 various stages, with illustrations, may be found in 

 the paper prepared by Mr. Wilson ^ at the St. An- 

 drews Marine Laborator}', already referred to. It 

 may be well to note that ]\Ir. \Mlson found ova and 

 spermatozoa, ' presenting no appreciable difference 

 from those taken from the full-grown adults,' in 

 mussels only one-eighth of an inch long. This 

 raises the question as to what a full-grown adult is. 

 Every^ one, we may presume, has a general idea 

 as to the average size of a mussel as used for 

 bait, or as seen growing on rocks on the coast, but 

 if inquiry be made into the sizes of mussels in 

 different localities it will be found that the result 

 is confusing. If a mussel becomes an adult 

 whenever it is capable of reproducing its species, 

 then we are safe in saying that adult mussels may 

 be found varying in size from one-eighth of an 

 inch to at least twice the size of what most people 

 would consider to be a full-grown mussel, or a 

 large mussel suitable for purposes of bait. Range 

 of mature size was shown to the writer some years 



^ Fifth Annual Report of the Fishery Board for Scotland, 1887, 

 Appendix F, No. vi. p. 247. 



