14 THE PHYSIOLOGY OF REPRODUCTION 



even in some cold seas periodicity is far more often eliminated 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. (Cf. p. 29.) 



ECHINODERMATA 



Sea-urchins and starfish, and other Echinodermata, appear gener- 

 ally to have a regularly recurrent breeding season, at which the 

 genital organs swell up to an enormous size. In the sea-urchin, 

 Echinus esculentus, these organs grow into huge tree-like 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. esculentus 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. 1 At 

 Dunbar, in Scotland, it has been observed to spawn at the same 

 time. The sea-urchins at Naples spawn at the end of the year 

 (E. acutus being mature in November and December, and E. micro- 

 tuberculatus from September onwards). 2 Fox has written as follows 

 concerning the Mediterranean and Eed Sea species : 



" The sea-urchins at Suez (Diadema serosum) breed from the 

 spring until September. During this season the genital products 

 are developed in cycles correlated with the lunar periods. Sperma- 

 tozoa and eggs are discharged into the sea between the first and third 

 quarters of each moon, the majority of individuals spawning about 

 the time of full moon. The greater number of specimens examined 

 between the first quarter and full moon have the gonads swollen and 

 filled with spermatozoa or eggs in a state ready for discharge into the 

 sea, while a smaller number show that the genital products have 

 lately been shed. As the third quarter of the moon approaches, 

 whereas some individuals still have testes or ovaries full of sperma- 

 tozoa or eggs, most have already spawned. After the third quarter 

 all have extruded their genital products, and the gonads, now smaller 

 in size, contain numerous spermatocytes or oocytes in the process of 

 development into spermatozoa or eggs, to be shed into the sea round 

 about the next full moon. From the new moon until the first 

 quarter following it the gonads are filled with spermatocytes or 

 oocytes in a more advanced stage of development, and, in addition, 

 there are present in some individuals spermatozoa and unripe or ripe 

 eggs. After this the same cycle is repeated. 



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

 Echinus, Liverpool, 1900. 



2 Lo Bianco, loc. cit. The spawning times of most of the Naples Echinoderms 

 are given in these memoirs. 



