480 F. A. POTTS. 



fertilisation. A. H. Cooke quotes two cases in the Cambrid<,'e 

 Natuial History, volume " Molhiscn/' In both Arion ater and 

 Liiinasa auricularia, individuals isolated from birth pro- 

 duced fertile spawn, although in somewhat limited quantities. 



In the Annelids a case has recently been described by 

 Pierautoni^ in Protodr i I us. Ova are developed in the ante- 

 rior seg'uients, spermatozoa in the posterior, and a large pro- 

 portion ot:' the former are fertilised while still in the body- 

 cavity. There is, however, a second method of reproduction, 

 when by the rupture of the body-wall of the hermaphrodite 

 the whole number of the eggs is discharged into the sea. At 

 the same time certain male individuals commonly occurring 

 in the species emit their spermatozoa, which unite with such 

 eggs of the hermaphrodite as have escaped self-fertilisation. 



In the Crustacea heruiaphroditism is largely developed in 

 two groups, the Isopoda and the Cirripedia, la the former, 

 the production of the spermatozoa in each individual precedes 

 that of the ova, and the absorption of surplus spermatozoa 

 by phagocytes may preclude the possibility of self-fertilisation 

 (e.g. Danalia-). In the cirripedes adjacent individuals 

 normally cross-fertilise; a single case of self-fertilisation was 

 recorded in Pollicipes (Gruvel). In the curious parasitic 

 group, the Khizocephala, both Saccnlina and Peltogaster, 

 invariably practise self-fertilisation.'' 



Great interest attaches to the restriction of sperm-produc- 

 tion accompanying the condition in this group. A small part 



and the Rliizocepliala. the self-fertilisation which they practise is 

 evidently a secondary and adaptive phenomenon. In the first two cases 

 it has been developed as a means hj wliich the actual existence of the 

 race may l^e safeguarded, for Ijoth classes of creatures are liable to 

 sudden extinction by the desiccation of the pool or moist soil, where 

 they respectively live, and it is a manifest necessity that an isolated 

 survivor should be callable of independent reproduction when conditions 

 again become favoural 'le. 



1 -Fauna ii. Flora Golfes von Keapel.' t. 31. " Protodrilus." 1908, 

 pp. 117-119. 



= G. W. Smith. ' Faiina u. Flora Golfes Xeapel" Mon. 29, • Rhizo- 

 cephala,' 1906, p. 101. 



=> G. W. Smith, loc. cit.. pp. 21-2^. 



