﻿138 Proceedings of the Royal Physical Society. 



difficulty in Dr Marshall's case is to know to what extent, 

 if at all, boxfuls sent to the Laboratory are selected material, 

 since they are bought at Newhaven fish-market. The same 

 difficulty applies to the 1359 "Zool. Lab." specimens which 

 are here dealt with, and an examination of the numbers in 

 the different boxes shows how variable is the proportion of 

 the sexes. There were altogether 110 females in this 

 collection, or just over 8*2 per cent., compared with Dr 

 Marshall's 6*4 per cent. Yet the percentages in the different 

 boxfuls varied from less than 1 to nearly 14. On the 

 whole, however, the results are fairly consistent. But there 

 does not seem, at least at first glance, to be much consist- 

 ency in the proportion of the sexes in many of the lots 

 outside the University collections. And yet we are here 

 surer of our facts, since we know that these specimens at 

 least (lots A to H) were taken at random. 



It is when we examine the total number of (a) males and 

 (h) females in (1) catches taken by the ordinary trawl, and 

 (2) catches taken by small-mesh net or by small trawl, 

 that a possible explanation appears. From Table III. it is 

 seen that of lots A to H, altogether 4216 Nephrons were 

 captured in the large trawl, and 319 in the small-mesh net 

 {i.e., " escapes " from the large trawl) or in the small trawl. 

 There are 469 females, or over 11 per cent., among the 4216 

 captured by the large trawl, against 124 females, or about 

 43*5 per cent., among the 319 captured by the smaller mesh 

 nets. It is also significant that in one case, lot A, haul 7, 

 the females actually outnumber the males ^ and that here the 

 small trawl was used. (It is very probable that the size of 

 the mesh, which was smaller than that in general use by 

 trawlers, may account for my finding about equal numbers 

 of males and females in 656 Norway lobsters dredged in the 

 Clyde in September 1903.) From all this it may perhaps 

 be inferred that, while, as a matter of fact, more males than 

 females are caught, this may be accounted for partly by the 

 method of capture, for males, being larger than females, 

 may (1) be caught in greater numbers owing to size of 

 mesh used, and (2) be kept by fishermen while smaller ones 

 are rejected as unsaleable. 



