l62 BENNET M. ALLEN. 



be displaced by this work of dissection. Preparations were pre- 

 served in formalin or alcohol. 



The material to be sectioned was hardened in 3 per cent. 

 chromic acid for a day or two, and after the usual washing and 

 dehydrating, cleared in xylol and embedded in soft paraffine. 

 Very thick sections were cut, cleared in xylol and mounted 

 serially in Canada balsam. They were studied under a dissecting 

 microscope with fairly high power lens. The relation of particu- 

 lar organs to the limits of the rings was carefully estimated by 

 placing under the slide a piece of thin paper with straight ink- 

 marks across it. 



There was considerable variation in the position of the nerve 

 ganglion with reference to the sensory ring of the somite to 

 which it belonged. From a table of measurements I selected 

 the specimen which showed an average position of the ganglia. 

 The three ganglia in this specimen (K) all projected beyond the 

 anterior limit of the sensory ring to which they belonged, and 

 lay largely in the fifth ring of the preceding somite. The propor- 

 tion thus found in front of the limit of the somite was 0.7 in the 

 case of the ganglion of the sixteenth ; 0.8 for that of the seven- 

 teenth ; and likewise 0.8 for the ganglion of the eighteenth 

 somite. The observations extended over a series of thirteen 

 specimens. The measurements, similarly taken in all specimens, 

 were as follows : 



Somite. i6th. ijth. i8th. 



A i.o 0.6 



B i.o 0.8 i.o 



C i.o i.o i.o 



D 1.4 J -3 l - 



E 0.6 0.7 



F 0.6 0.6 0.8 



G 0.7 1.8 1.6 



H 0.5 0.5 0.8 



I 0.7 0.8 0.5 



J o.o 1.2 1.7 



K 0.7 0.8 o.S 



L 0.5 0.8 



M 0.3 0.7 0.9 



NOTE. No. i.o indicates that the ganglion in question lies 

 wholly within the fifth ring of the preceding somite ; a decimal 



