Mr Punnett, Note on the proportion of the sexes etc. 293 



Note on the proportion of the sexes in ' Carcinus maenas.' 

 By R. C. Punnett, M.A., Gonville and Caius College. 



[Received 23 November 1903.] 



It has been recently suggested by Bateson 1 that Mendel's Law- 

 may apply to the phenomenon of sex heredity. If such is the 

 case Castle 2 has shewn that in the $s of most dioecious animals 

 we must assume the existence of two kinds of ova, in which the £ 

 and % elements respectively are dominant ; and a similar state of 

 things must also hold good for the spermatozoa. If this segre- 

 gation of characters (</ and % ) occurs in some cell division prior 

 to the formation of the primary oocyte (or spermocyte), it follows 

 that the number of ova exhibiting </ dominance produced by any 

 % must be numerically equal to the number of ova shewing % 

 dominance ; and similarly for the spermatozoa produced bya (/. 

 Consequently we should expect to find the two sexes existing in 

 equal numbers if the conditions of life are similar for each. Where 

 the numbers are unequal we should most naturally turn for ex- 

 planation to the possible existence of a different rate of sexual 

 mortality. The evidence for or against the operation of this 

 factor must depend upon our knowledge of the proportion of the 

 sexes at different stages in the life- history of a species ; and it 

 was with a view to obtaining such evidence that the following 

 statistics relating to Carcinus maenas were brought together. 



The crabs here dealt with were collected on a small area of 

 the coast of Guernsey at the southern extremity of Rocquaine 

 Bay during the 2nd and 3rd weeks of June in the present year. 

 They occurred here in great abundance, due doubtless to the 

 fact that the area in question was that selected by a neighbouring 

 hotel for the deposition of its garbage. The stones of the area 

 (which lay in and rather above the Fucus zone) were systematically 

 overturned, and the few inches of dirty sand found beneath most 

 was carefully dug up. Practically every crab seen was captured 

 and slain prior to the determination of its sex and maximum 

 carapace breadth. The majority of the specimens collected on 

 this area were adult, and few occurred whose carapace breadth did 

 not exceed 10 mm. Smaller specimens were found much more 

 abundantly nearer high-water-mark at a spot a few hundred yards 

 along the coast in the direction of the lighthouse. These were 

 preserved in formol and sorted later according to size, after which 



1 Bateson, W., and Saunders, E. E., Reports to the Evolution Committee, No. 1, 

 London, 1902. 



2 'The Heredity of Sex,' Bulletin of Museum of Comp. Zoology from Harvard 

 CoUege, 1903. 



