NERVE CELLS OF THE CRAYFISH 39 
as that of recognized structural elements in the living cytoplasm, 
but one, nevertheless, upon which a stable scientific superstruc- 
ture may be erected. If Nissl bodies, neurofibrillae, etc., are 
made evident in various cells by the same technic, whether these 
be artefacts or not, the observer is justified in the opinion that 
there is probably also a similarity between the cells in the living 
condition. 
MATERIAL AND METHODS 
The nerve cell of the crayfish serves well as a subject for 
cytological study. Material is readily obtained and but little 
work has been done upon it. The ventral ganglia with their 
large cells are so easy of access that no postmortem changes 
need occur. Only two or three minutes are needed for the killing 
of the animal and the removal and transfer of the cord to the 
fixing solution. The large cells lend themselves especially well 
to the study of the trophospongium and of the origin of the 
axis cylinder. 
Most of the material used was from young specimens and 
adult specimens of Cambarus soon after they were collected in 
the field. Practically all of the current neurocytological methods 
were tried, but only the following yielded results at all satis- 
factory. 
1. Intravitam staining 
After intravitam staining with thionin or methylene blue the 
neurofibrillae could be clearly seen in the fresh teased material. 
A .01 per cent aqueous solution of thionin or methylene blue 
was injected into the pericardial sinus. Upon the death of the 
animal, twenty to sixty minutes later, the abdominal nerve 
cord was removed into a thionin solution of the same or double 
strength and teased. For thirty minutes after removal no 
postvital changes were usually noted so that there was oppor- 
tunity to study the cells with some care. 
2. Silver methods 
All of the silver methods proved to be exceedingly fickle. 
There were striking differences between the reactions obtained 
in young animals 4 to 53 em. long, and those obtained in adults. 
