THE BREEDING SEASON 15 



ture. Semper ^ says that few things impressed him more in the 

 Philippine Islands than the absence of all true periodicity in the 

 breeding habits not only of the land-molluscs, but also of the 

 insects and other land-animals. "I could at aU times find 

 eggs, larvae, and propagating individuals, in winter as well as in 

 summer. It is true that drought occasions a certain periodicity, 

 which is chiefly perceptible by the reduced number of in- 

 dividuals in the dry months, and the greater number in the 

 wet ones ; it would seem that a much smaller number of eggs 

 are hatched under great drought than when the air is very 

 moist. Even in January, the coldest and driest month, I found 

 land-snails which require much moisture, and at every stage 

 of their development, but only in shady spots, in woods, or by 

 the banks of streams. But what was far more striking in these 

 islands was the total absence of all periodicity in the life of the 

 sea-animals, particularly the invertebrata ; and among these I 

 could not detect a single species of which I could not at all 

 seasons find fully grown specimens, young ones, and freshly 

 deposited eggs." Semper goes on to remark that even in 

 some cold seas periodicity is far more often ehminated than is 

 commonly supposed, and mentions that the eggs of the sea- 

 mollusc, Tergipes, have been found at all seasons, like those of 

 Littorina on our own coasts. 



ECHINODEEMATA 



Sea-urchins and starfish, and other Echinodermata, appear 

 generally to have a regularly recurrent breeding season, at 

 which the genital organs swell up to an enormous size. In the 

 sea-urchin. Echinus esculerUus, these organs grow into huge 

 tree-hke structures with branched tubes, lined by the sexual 

 cells. These are sold for food by the fishermen in Naples, who 

 call them " frutta di mare." It is said that a single female 

 E. esculentiis will produce as many as 20,000,000 eggs in a 

 breeding season. At other times of the year the generative 

 organs are so reduced as to be scarcely recognisable. E. esculentus 

 at Port Erin, in the Isle of Man, spawns in June.^ At Dunbar, in 



' Semper, loc. cit. 



* Chadwick, Liverpool Marine Biological Committee Memoirs, vol. iii., 

 Echinus, Liverpool, 1900. 



