SEXUAL COLOKATION. 275 



(see p. 229) should be made upon these spiders. M. Plateau 

 thought himself justified in stating that hunting spiders, 

 belonging to the same family as some of those treated of by 

 Mr. and Mrs. Peckham {Attidce), could only distinguish their 

 prey well enough to capture it at a distance of from three- 

 eighths to three-fjuarters of an inch ; and even, at that short 

 distance, their vision was not accurate, since mistakes were 

 frequently made. It should also be shown that blinding the 

 sjiiders put an end to any selection. Until such experiments 

 have been made, it is premature to draw too detailed con- 

 clusions from the very interesting facts which the two 

 memoirs contain. 



On the other hand. Dr. Mc(Jook * quotes experiments which 

 ■seem to indicate that the Saltigrades can see for a distance 

 of ten inches or so. In fact, observations on this exceedingly 

 important subject are most contradictory. 



Sexual DimorpMsm partly due to a Need for Protection on the 

 part of the Female. 



Mr. Wallace, in criticising the theory of " sexual selection," 

 has offered two alternative views of sexual dimorphism, which 

 are not necessarily opposed to each other ; they might both be 

 accepted. In Darwin's theory, stress is laid upon the brilliant 

 colours of the male birds, and it is to be inferred that originally 

 both sexes were similarly and plainly coloured, that coloration 

 being often retained in the female. It is perfectly true that 

 the male sex is in many respects the most specialised ; in many 

 animals with a pronounced sexual dimorphism, the young 

 males are like the females ; it is only on the approach of sexual 

 maturity that the distinctive secondary attributes of the male 

 are acquired. 



* ■" American Spiders and their Spinning Work.'' 



