Turner, Mushroom Bodies of the Crayfish. 343 
Although the above enumeration of nerves agrees per- 
fectly with KRIEGER (88), yet students of invertebrate neurol- 
ogy will notice at once that it does not tally with Yune (’78) 
who describes seven pairs of cranial nerves. One of the nerves 
mentioned by YunG which is not included here is the nerve to 
the frontal organ. Although occasionally I have thought that 
I detected a small nerve passing from the front of the brain to 
the rostrum, yet I have not been able to demonstrate, to my 
own satisfaction, the existence of such anerve. The other 
nerve not included here is the antennulo-motor nerve. Al- 
though it stands to reason that there must be an antennulo- 
motor nerve, yet I have not been able to differentiate it from 
the main antennulary nerve. The following comparative table 
will emphasize this point. 
CRANIAL NERVES OF THE DECAPODS. 
Yung Krieger This paper 
To frontal organ R P 
Optic Optic Optic 
Oculomotor To eye muscles Oculomotor 
To antennules 
os Se Ist antennary Antennulary 
To muscles of the 
antennules 
Tegumentary Tegumentary Tegumentary 
|- : 
To the antenna 2nd antennary Antennary 
In this paper it is not thought wise to attempt to point 
out homologies between the cerebral nerves of the crayfish and 
those of the Aznelda. 
Cet NIDI. 
In the Decapod brain, the following eight clusters of nerve 
cells are easily recognized: an unpaired dorsal nidus, a pair of 
inner mushroom nidi, a pair of outer mushroom nidi, a pair of 
_latero ventral nidi, and an unpaired ventral nidus. In addition 
to these cell clusters, neuroglia cells are scattered throughout 
the brain. In some regions the cells are collected in clusters. 
