The eyes which occur in Polyclads may be divided into (_a_) a pair of cerebral groups overlying the brain; (_b_) those embedded in the tentacles (tentacular group); and (_c_) the marginal eyes, which in _Anonymus_ occur all round the margin. A complex form is sometimes assumed by the cerebral eyes of Pseudoceridae, resulting probably from incomplete fission (Fig. 11). _Leptoplana otophora_ was obtained by Schmarda on the south coast of Ceylon. On each side of the brain is a capsule containing two otoliths. This is the only known case of the occurrence of these organs in Polyclads. REPRODUCTION.—Although Polyclads are able to repair the result of injuries to a very considerable extent, they are not known to multiply asexually. The two processes are intimately associated, but, though probably all Turbellaria can regenerate certain lost parts, asexual reproduction only occurs sporadically. {27}[Illustration: FIG. 11.—Double eye from the cerebral group of _Pseudoceros maximus_. (After Lang.)] All known Polyclads are hermaphrodite. The male organs, scattered, like the testes of _Leptoplana_, over the ventral surface, 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 _Leptoplana_ (Figs. 2 and 5, ♂ and ♀). In _Trigonoporus_, a genus once found at Naples, a secondary female aperture has been discovered leading into the female genital canal[35]; and in _Anonymus_, _Polypostia_, and _Thysanozoon_ (Fig. 7, E, ♂) 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,[36] belonging to the Acotylea, possesses 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 (_Yungia_) that happened to cross its path, spermatozoa being of course left in the wound. Lang further found that _Prostheceraeus albocinctus_ 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 impregnation" occurs sporadically in several groups of animals.[37] {28}Nevertheless, in some Polyclads it is probable, and in _Stylochus neapolitanus_ it is certain, that normal copulation takes place. The sperm-masses are transferred to a coecal diverticulum of the female genital canal, and then by a delicate mechanism, of which we know only the