372 Proceedings of the Royal Physical Society. 



muscles of Zumhricus. It seems very curious that species of 

 the same genus sliould differ so markedly in an anatomical 

 character, which would seem a priori to be of considerable 

 importance ; and it is still more curious that P. hasseltii and 

 A. capensis should agree with each other, and with a distinct 

 genus Liimbricus, and differ from the other members of their 

 own genus; such facts might be supposed to indicate that 

 the bipinnate arrangement of the muscles represented a 

 primitive condition which has been retained here and there 

 but lost in the majority of earthworms. Perrier, however, 

 states that such is not the case, and that the young of 

 Lumhricus present no traces of the bipinnate arrangement of 

 the muscles of the adult.^ 



While writing this an interesting paper by Dr E. Eohde ^ 

 upon the muscles of Annelids has come into my hands. This 

 anatomist has studied the structure of the body wall in a 

 great number of different worms belonging both to the 

 Oligochseta and the Polychseta. It appears from his observa- 

 tions that the genus Lumhricus, like Perichceta and Acantho- 

 drilus, does not present an absolute uniformity in the 

 structure of the longitudinal muscular coat. Certain species 

 agree with Luinhricus terrestris in the regular arrangement of 

 the fibres, while L. olidus differs entirely, and shows no 

 traces of the bipinnate disposition of the fibres, except close 

 to the line of junction with the circular muscular coat. 



Acanthodrilus was instituted as a genus of earthworms by 

 M. Perrier in his "Eecherches pour servir a I'histoire des 

 lombriciens terrestres." ^ It is to be distinguished from the 

 other genera of the group " Postclitelliens " by the presence 

 of four male generative apertures situated in pairs on the 

 17th and 19th segments of the body or in their immediate 

 neighbourhood. With each of these apertures is connected 

 a simple coiled tube — the prostate gland — and a saccular 

 diverticulum, enclosing two or a greater number of peculiarly 

 modified penial setae. Three species were described by M. 

 Perrier ; two of these — Acanthodrilus ohtusus and A. ungu- 



1 Arch. d. Zool. Exp., t. iii., p. 387. 



2 Zool. Anzeig., No. 189 (1885), p. 135. 



3 Nouv. Arch. d. Museum, 1872. 



