170 ME. r. M. CAMPBELL OK THE 



scarcely be suspended for a longer period than necessary for the 

 sexual union. Spiders frequently eat one another; and such an 

 occurrence after pairing is only curious if considered apart from 

 their habits. When the sexual desire is satiated, their actions 

 would be again directed by the dominant instinct of destruction, 

 which would be stronger if a general excitement be supposed to 

 follow the union. 



The excellent means which spiders such as T. Guyonii possess 

 of measuring each other's strength when on the same web by the 

 tension and motion of the threads, are calculated to prevent an 

 attack except by the stronger or through blind fury. Now the 

 comparative size of the sexes of this species varies considerably*. 

 It is not unusual to find a large male, with its longer legs, much 

 more formidable in appearance than a small female of recent ma- 

 turity ; and such was the case in the three attacks on the female 

 and in the lengthened courtship above mentioned. 



The same caution or, one might say, self-restraint shown by 

 spiders in hesitating before springing on a hopelessly entangled 

 defenceless insect larger than their usual prey, seems equally dis- 

 played in conflicts between themselves. Blind fury is not there- 

 fore always the actuating impulse. 



It will be observed that the attack, when made by a female, 

 often follows the union immediately, while that of the three 

 males took place some time afterwards. The explanation ap- 

 pears to be this : — The action of a female when satiated would be 

 precipitated by the threatened and unacceptable continued appli- 

 cation of the hard spiny palpus, while the more lasting desire of the 

 male would have to subside before he became directed by another 



* Simon ('Les Arachnides de France,' vol. ii. pp. 60 & 61) gives the following 

 measurements : — 



cJ. Ceph., lengtli 8-5 mm., breadth 7; legs, 1st 74-6, 2nd 63-6, 3rd 45, 

 4th 68-2. 



$ . Ceph., length 8 mm., breadth 6 ; legs, Ist 46, 2nd 40-2, 3rd 36, 4th 44. 

 Abd., long. 11, larg. 8. 



S min. Ceph. long. 4'5 ; § min., long. 6. 



The wandering sexual excursions of the males may have developed the greater 

 length of legs, while the necessary additional weight of the abdomen of females 

 must have aflFected the cause and sum of natural selection in this respect. The 

 ordinary habits are the same with both sexes. 



The sexual excursions of the Argyronetica aqiiatica may have been a larger 

 factor in the development of the greater size of the male as compared with the 

 female. The passage through water, which is the habitat, would require more 

 strength than on land. 



