94 On the genus Onchidium. [No. 2, 



specimens the vas deferens was in the terminal half of its length filled 

 with a similar colouring fluid which I have noticed in the receptaculum 

 seminis ; thus it is not likely that this substance is secreted in the 

 latter organ, but more likely is formed in the internal portion of the 

 vas deferens. Close to the opening of the male genital pore, terminates 

 the supplementary albuminous string (ps), varying from 9 to 10 

 inches in length. It is much thicker than the vas deferens and the 

 contents is a purely white granular, moderately viscous substance. 

 In some other species, this albuminous string is still longer and more 

 developed. 



I have only once (on the 22nd September,) observed two speci- 

 mens of Onchidium typhce in copulation, they were seated one behind 

 the other, the penis enclosed in the vagina for about the length of one 

 inch. Reciprocal impregnation at the same time, as known in Limaces, 

 does apparently not take place. Buchannan's statement on this point 

 is not clear ; the error as to his believing the sexes to be divided in 

 . two animals is thus readily explained, and would have then been easily 

 corrected, had he examined the internal organisation. But although 

 he states that " during copulation the distinction of sexes is very 

 evident, the penis protruding to a great length," it would appear from 

 his previous statement to the effect that " in both, the anus and sexual 

 organs are placed in a perforation in the under part of the tail" as 

 if he had observed that the copulative organ were also situated 

 posteriorly. This is undoubtedly an error, and can only be explained 

 by the fact that the anterior and posterior end were mistaken one for 

 the other, they being actually undistinguishable in a dorsal view 

 when the animal is resting quietly, and has the pedicles and the head re- 

 tracted, which position it actually assumes during copulation. I men- 

 tion this point in particular, because it appears to have been accepted 

 by several authors in its integrity, as recorded by Buchannan, though 

 its correctness was rightly questioned by others. Undue importance 

 has been attached to it, so as to support the presumed generic distinc- 

 tions of Onchidium, Oncliidella and Peronia. 



The Onchidia in general are to all appearance oviparous, laying 

 their eggs in damp places, either under stones or in holes near the 

 surface of the ground, where I found in large numbers very young 

 specimens, resembling in all external characters the full grown 



