ANATOMY OF POLYCLAD1DA 



27 



develop earlier than the ovaries, though the periods of maturation 

 overlap ; hence the possibility of self-fertilisation, though remote, 

 is still worth consideration. The genital apertures, through 

 which, in the male, spermatozoa, and in the female, ova, are 

 emitted, are usually situated as in L&ptoplana (Figs. '2 and 5, 

 c and ? ). In Triyonoporus, a genus once found at Naples, a 

 secondary female aperture has been discovered leading into the 

 female genital canal 1 ; and in Anonymus, Polypostia, and Thysa- 

 nozoon (Fig. 7, E, 6) two or more male pores and penes have 

 been found. Anonymus has several penes (Fig. 7, D, <) 

 arranged radially round the body. Polypostia, a remarkable form 

 described by Bergendal, 2 belonging to the Acotylea, possesses 



Fig. 11. Double eye from the cerebral group of Pseudoceros maximits. (After Lang.) 



about twenty such structures ranged round the female genital 

 aperture. Lang, whose attention was attracted by these singular 

 facts, made the interesting discovery that Thysanozoon uses its 

 penes as weapons of offence rather than as copulating organs, 

 burying them in the skin of another Polyclad {Yung in) that 

 happened to cross its path, spermatozoa being of course left in 

 the wound. Lang further found that Prostheceraeus cdbocinctus 

 and Cryptocelis alba in this way implanted a spermatophore in 

 the skin of another individual of the same species, and he 

 suggested that from this point the spermatozoa wandered through 

 the tissues till they met with and fertilised the eggs. It 

 is now known that a similar process of " hypodermic impreg- 

 nation " occurs sporadically in several groups of animals. 3 



1 Lang, " Pohjcladcn," PL 30, Fig. 8. 



2 Kongl. Fysiograf. ScUlskapets Kandlingar, Bd. iv. Lund, 1892-9-3. 



3 Whitman, Journal of Morphology, vol. iv. 1890, \>. 361. 



