MORPHOLOGY OF THE AMPHINEURA. 221 



far more considerable ; but still, notwithstanding the light which 

 has been thrown upon this subject by the researches of Hansen, 

 Sedt'wick, and others, different details as yet only repose upon 

 insufficient evidence (strengthened though it may be by ingenious 

 speculations), and should be re-examined whenever specimens 

 of these very rare species are available. 



In the following short account I will try to give a fair valua- 

 tion of the statements of the different authors, at the same time 

 endeavouring to hold myself free from any preconceived opinions 

 on the subject. 



If we except Graff's account of the genital organs and the 

 oogenesis of Chatoderma (3), which, however, has afterwards 

 been criticised and corrected by Hansen (6), all authors unani- 

 mously place the genital gland of the different genera of Amphi- 

 neura in the median line of the dorsum, immediately below the 

 integument, and with only the median dorsal blood-vessel 

 superior to it. The genital gland stretches throughout the 

 greater part of the length of the animal, is more or less sym- 

 metrical, and was found in Proneomenia (7) to be regularly split 

 up ventrally into two halves, and to have a multilobate appear- 

 ance. The sexes are separate in the Chitons (10, 19) and in 

 ChcBtoclerma (6), whereas Neomenia and Proneomenia appear to 

 be hermaphrodite (7, 11). The latter genus, however, has as yet 

 never been examined in the fresh state. 



With respect to the way along which, in the Chitones, the 

 genital products travel outwards, certain divergent opinions have 

 to be recorded in succession. According to the researches of 

 Cuvier (1), Middendorf (16), von Jhering (10), and Sedgwick 

 (19), there are two ducts, a left and a right one, which leave 

 the genital gland on the dorsal surface, close to its posterior ex- 

 tremity, and strike for the branchial furrow, into which they 

 open between a pair of the posterior branchise. This passage is 

 coiled in the female, straight in the male (19). I have myself 

 been able in sections to further confirm the presence of the same 

 arrangement in Chiton mar ginatus. Hall (2) has noticed certain 

 different modes of egress for the genital products, and mentions 

 the presence, in some species, of a simple genital pore, in others 

 of a fenestra, i.e. of a slit which is divided by bridges of tissue 

 into from two to seven openings. Not finding an oviduct in 

 the latter case, he is inclined to suppose that the eggs are set 

 free in the body-cavity, and from thence pass outwards through 

 these fenestrse. These observations are in great need of further 

 confirmation. 



Before passing on to the genital apparatus of the Soleno- 

 gastres I hold it to be appropriate to mention the renal or 

 excretory apparatus of the Chitones, as these two systems, which 



