202 MB. A. D. MICHAEL OS AN [Mar. 5, 



existence might be anticipated ; it will be seen by fig. 20 that I find 

 more than one branch to each leg of the two hind pairs, in the 

 fourth leg in particular I find several branches. 



Croneberg, Schaub, and Nalepa all found that each of the four 

 leg-uerves on each side of the body was accompanied by a much 

 smaller nerve running parallel to it, which they call the accessory 

 nerve ; they all describe and figure it, doubtless correctly, as 

 springing from the brain itself. In the pi'esent species the 

 arrangement is very difi'erent ; in the first two pairs of legs these 

 accessory nerves exist (fig. 20, na.), and may be plainly seen in 

 dissections although they are small and fine ; but they do not sprinc/ 

 directly from the brain as in the cases observed by those authors : 

 they spring from the respective principal leg-nerves a short 

 distance from the brain, and are in fact the first branches of those 

 nerves ; indeed the only ones which I have traced, although 

 probably others exist iu the more distal parts of the principal 

 nerve. The two hind pairs of legs are entirely without accessory 

 nerves, either springing from the brain or from the principal 

 nerves. It is true that branches a good deal like the accessory 

 nerves in character spring from the principal nerve much further 

 on its course (fig. 20, n 3, n 4), but they are so very much further 

 away from the brain than the branches of tlie nerves of the two 

 first pairs of legs, that they can hardly be considered the homologues 

 of the accessory nerves ; moreover these branches are paired, not 

 azygous as the accessory nerves are. No one has traced the 

 accessory nerves to their destination or offered any explanation 

 of what they are. It seems to me that the present species 

 probably affords the key to this problem ; they are apparently 

 really branches of the principal nerves, which, in the species 

 described by Croneberg and others, and probably in the majority 

 of allied species, have for some reason gradually come to spring 

 more and more closely to the brain until at last they have ended 

 by springing from the brain itself and not from the principal nerve 

 at all. 



The last pair of large nerves springing from the lower ganglion 

 are a pair quite at the rear and near the median line (fig. 20, n^.), 

 which innervate the genital organs ; practically all authors are 

 agreed upon this point. In the present species I find that the 

 principal trunk of the nerve runs to the dorsal side of the genital 

 apparatus, and there gives off numerous fine branches to the 

 various parts ; and also sends a large branch to the vagina or ductus 

 ejaculatorius and penial canal, as the case may be, and the muscles 

 which surround it; and this branch divides, sending secondary 

 branches to the so-called genital suckers. The principal branch 

 forms a distinct ganglion, from which the fine nerves that are 

 distributed to the organs actually arise ; and there are at least one 

 or two small ganglia in connection with the larger trunk. The 

 existence of such ganglia has been already indicated by Schaub 

 p,nd even by Pagenstecher in 1860, The branches from this 



