The Stickleback. 167 



sexes differ but little ; in others the sexual differences 

 become greater, and the male is only one-third the 

 length of the female, but in some of them the dispro- 

 portion is greater still. At the same time, we see 

 nematodes where males are attached to the females, 

 so as to appear to form only one single individual ; 

 in other cases the male seems to disappear to such an 

 extent that we find nothing but the male organ in the 

 female ; indeed there are instances of male worms 

 which, without changing their form, occupy the cavity 

 of the matrix, and, like the learnean crustaceans, are 

 parasites of their females." * 



Reproduction in certain circumstances shortens life. 



" The American aloe reproduces and dies in about 

 five years in Mexico ; in England it elaborates leaves 

 for a hundred years before flowering. Again, the 

 axolotl reproduces in warm Mexico as a branchiferous 

 amphibian ; in colder climates its fertility is dimin- 

 ished, it becomes salamandroid before reproducing, 

 thus lengthening life by delaying genesis." t 



Then, for another instance, take the stickleback : 

 he is a great fighter, armed and plumed and mailed 

 cap a pie, and this because he is a determined poly- 

 gamist — he is perhaps the most plucky fighter of all 

 fishes — the more he fights the more colour he gets, 

 as though into him passed all the hues of all the 

 enemies he had conquered, and this because he must 

 secure many wives, as many as stock fully his open- 

 ended barrel-built nest with eggs. And the moment 

 his fighting and breeding are ended he subsides into a 

 commonplace little stickleback ; he waxes thin and 



* Parasitic Animals, p. 235. 



f Ray-Lankester's Longevity, p, 85. 



