180 :.': S- <5oto. 



missures occurring nearly at regular intervals ; and in such a 

 way that each commissure between the ventral nerves lies in a line 

 with that between them and the ventro-lateral nerves. The ventro- 

 lateral nerves, atrain, sends ont branches towards the lateral margin 

 of the body, just at those points where they receive the commissures 

 from the ventral nerves ; so that all the nerves form a regular I'ect- 

 angular net-work, and divide the whole ventral surface of the body 

 into a number of distinct areas. At the points where the commis- 

 sures cross the main nerves, the course of the fibres is interesting. 

 From any main nerve, namely, which we may be considering, fibres 

 are given otf on both sides to the neighl^oring nerves. Beside these, 

 there are also fibres coming from the latter and proceeding directly 

 past the main nerve without mingling with its fibres, so that the 

 four main nerves are probably ])ut in direct connection with one an- 

 other. I ha\e counted as manv as thirteen commissures in the an- 

 terior half of the body, in addition to the pair of commissures between 

 the anterior nerves. In the posterior half the commissures seem to be 

 less numerous. I have l^een able to count only a few ; but this is 

 perhaps due to the presence of the strong fields already mentioned 

 and the special development of the diagonal muscle in this region, 

 which greatly increases the difficulty of following the course of the 

 nerves. I have not been able to make out the ])lexus whicli the 

 nerves probably f )rm on the dorsal side. 



As to their histological character, tlie nerves present typical 

 "Balkenstränge" (Fig- 16)- In some of the meshes are to be seen 

 sections of nervous fibrils as exceedingl}^ miiuite dots, which are 

 visible only in the most favorable cases. Pintner'* maintains that 

 the " Biilkchen selbst" which form ilie mesh-work are the sections of 

 the fibrils which are probably arranged "reihenweise, nebeneinand- 



1) Pintner — I.e. p. 71. 



