The Retina and Optic Ganglia in Decapods, especially in Astacus. 3 
The following Dotes on the methods that I employed may be of 
assistance to those who undertake similar studies. 
The rapid Golgimethod as described by Kölliker (91, pag. 9) 
yielded good resiüts when applied to the optic organs of the crayfish, 
especially when the modification suggested by Ramon y Cajal was 
adopted and the preparations , after having passed once through the 
silver bath, were again put into the solution of osmic acid and 
potassic bichromate, and then reimpregnated with silver. A third or 
even a fourth application of the silver solution seemed often advan- 
tageous. On the whole, better results were obtained from material 
imbedded in paraffine than from that in celloidin. 
In preparations made by the Golgi method, the ganglion cells 
were colored less frequently than the nerve fibres or their terminal 
fibrillations. The relatively large size of the nerve fibres and the 
peculiar course that they took through the ganglia made it often 
difficult to prepare sectious in which the entire extent of a given 
fibre was shown, but this difficulty was due rather to the peculiar ana- 
tomy of the ganglia than to any defect in the method. For the 
study of the finer structure of the rhabdome, the Golgi method was 
invaluable. 
In employing methylen blue, I followed the general directions 
given by Retzius (90, pag. 24). For each crayfish experimented 
upon, about one tenth of a cubic centimeter of a 0.2^ aqueous 
solution of methylen blue was injected into the ventral blood sinus. 
Animais thus treated seemed to suffer no inconvenience, and, after 
being kept a week or so under normal conditions, they usually lost 
all traces of the blue coloration. When, however, they were killed 
and dissected some twelve or fifteen hours after they had been in- 
jected, many of the nervous elements were found to be colored in- 
tensely blue. The elements in the optic ganglia were less frequently 
stained than those in other parts of the nervous System, but among 
a dozen injected specimens there were always some three or four 
in which the optic ganglia were favorable for study. The ganglia 
in these animals were carefully removed and studied at once in the 
fresh condition, camera drawings being made of the more fully stained 
parts. It was necessary to do this without loss of time; for, soon 
after the death of the animal, the shafply differentiated blue stain 
begins to disappear, in part perhaps by fading, in part certainly by 
diffusion. Notwithstanding this drawback satisfactory results were 
easily obtained 
1 * 
