[nuPORTE] LARVA OF SPHIDA OBLIQUA WALKER 231 



majority of cases. This same writer also names several insects, 

 (mentioned by Kolbe) in which this cross-nerve originates from a 

 similar point. In the larva of the Sphinx ligustri L. however, ac- 

 cording to Newport, and in the majority of cases for which this nerve 

 has been described it originates from the brain. 



This nerve has been described for only a limited number of 

 insects, but, as Henneguy says, "elle doit se retrouver chez d'autres, mais 

 elle est très difficile a desséquer et à mettre en évidence." It was first 

 described for Crustacea by Audouin and Milne-Edwards in 1828. 

 At the time it was thought rather exceptional but the work of many 

 anatomists soon proved that it was also found in many insects and 

 its presence is now accepted as a general rule. 



No definite agreement seems to have been reached as to what 

 name should be given to this nerve. Several names have been used 

 by various writers, but none of them has been entirely satisfactory. 

 Some of the names most commonly used are, transverse commissure of 

 the oesophageal ring, les connexions transversales des commissures 

 oesophagiennes, commissure transversale and suboesophageal commissure. 

 Hammar, '08, adopts the term suboesophageal commissure, pointing 

 out that the other terms used are applicable only to a limited number 

 of cases. While this term is perhaps the most satisfactory in general 

 usage, and it is descriptive of the condition such as is found in the 

 Corydalis larva or in Sphida obliqua, it is however open to the same 

 objection as the other terms, because, as stated above, in the majority 

 of cases described, the nerve arises from the brain and passes around 

 the oesophagus. I have therefore used the term accessory commissure. 

 I believe that this term is applicable to all cases, and is descriptive 

 of the commissure in question as it distinguishes it from the main 

 commissures of the head, viz., the crura and the transverse commis- 

 sures which connect the ganglia that have fused in the formation 

 of the brain. 



The Suboesophageal Ganglion (Figs. 4, 7 and 8, S.G.) . This is a 

 large, somewhat egg-shaped ganglion situated beneath the oesophagus 

 in the posterior portion of the head, and connected with the supraoeso- 

 phageal ganglion by means of the crura cerebri as stated above. 



In this ganglion and the others of the ventral chain there is no 

 trace of commissures, 1 and the only indication of the duplicate chain 

 throughout this paper the term commissure is reserved for the transverse 

 connections between corresponding ganglia of the primitively double nervous chain, 

 while connective denotes the longitudinal connections between the ganglia of adjacent 

 segments. This uasge is in accordance with the suggestion of Yung, 78, and has 

 been adopted by Hammar and other writers. Dr. A. D. MacGillivray has however 

 suggested that the use of commissure has become so fixed in zoology as applying to 

 both transverse and longitudinal connections that it will be difficult to change it. 



