THE BREEDING SEASON 11 



live in burrows at the bottom of the water. With the attain- 

 ment of sexual maturity, and under certain peculiar conditions, 

 they swarm out for purposes of breeding. In the Atlantic 

 Palolo (Eunice fucata) and the South Pacific Palolo (Eunice 

 viridis) the process invariably takes place twice, upon or near 

 the day of the last quarter of the moon ; but with the former 

 species it occurs in June and July, and with the latter in October 

 and November. In the Japanese Palolo (Ceratocephale osawai) 

 the swarming takes place on nights closely following the new 

 and fuU moons (i.e. when the spring tides occur), in October 

 and November, the worms swimming out regularly four times 

 a year. Each swarming-period lasts from one to four days. It 

 has been noted further that the swarm is greater after the new 

 moon (when the spring tide is highest) than after the full moon 

 (when the tide is not so high), that each swarming takes place 

 invariably just after the flood in the evening, that it continues 

 for from one to two hours, and is generally larger on warm, 

 cloudy nights than on clear, chiUy nights. It would appear also 

 that no individual worm takes part in more than one swarming 

 in the year.^ 



Arthropoda 



Innumerable instances of the periodicity of breeding and its 

 relation to seasonal and environmental changes might be ad- 

 duced from the great group of Arthropods, but the reason for 

 the variations which occur is not always obvious. Thus, in the 

 common crayfish (Astacus fiuviatilis), in France the males are 

 said to approach the females in November, December, and 

 January, whereas in England they begin to breed as early as 

 the commencement of October, if not earlier.^ Also, in the 

 Cape species of Peripatus (P. capensis) birth takes place in a 

 fixed season (during April and May), whereas, in the South 

 American species, births are said to occur probably throughout 

 the entire year.^ 



In the case of the hemipterous insect known as the plant- 

 louse (Aphis), we have evidence that the mode of reproduction 



' Izuka, " Observations on the Japanese Palolo," Jour, of the College of 

 Science, University ofToTcyo, vol. xvii., 1903. 

 2 Huxley, The Grm/fish, London, 1880. 

 ' Sedgwick, "Peripatus," Oamb. Nat. Hist., vol. xii., Loudon, 1901. 



