TurRNER, Mushroom Bodies of the Crayfish. 333 
four pairs of nerves: labial, mandibular, labral, first maxillary 
and thoracic. The thoracic arises from the dorsal surface, the 
others from the ventral. | 
5. The second maxillary nerve arises from the first gan- 
glion back of the sub-oesophageal. 
6. From the last thoracic ganglion arises an unpaired 
abdominal and two pairs of leg nerves. 
7. There isa median compound triune eye situated near 
the dorsal surface. Each division of this eye is supplied with 
retinal cells anda lens. In most Cypride the optic nerve is a 
-median unpaired nerve which splits in three, branches, but in 
Notodromas there are three optic nerves. | 
8. Between the base of the antennz and the upper lip 
there is a pair of pear-shaped sensory organs, which are prob- 
ably.simple eyes. This organ is innervated by a branch of the 
labial nerve. 
9g. Bordering the mouth there are three pairs of similar 
sense organs which are innervated by branches of the labial, 
mandibular and labral nerves. The paper also discusses various 
sensory sete. 
Epear J. ALLEN (’96) discusses at length the histologica 
elements of the embryonic lobster and arrives the following 
conclusions: 
The thoracic ganglia are fused into one mass. 
A nerve cell with all its branches constitutes a unit. [This 
unit is called by many authors a neurone. | 
There are three main classes of neurones in the embryonic 
lobster brain: Ist, where all of the neurone lies within the cen- 
tral nervous system; 2nd, where the ganglion cell lies within 
the central nervous system and the fibers pass to the periphery; 
3rd, where the ganglion cell liés in the periphery and the fibers 
penetrate into the central nervous system. 
Class 1, which is composed of coordinating elements, is 
subdivided into four subclasses: A, where the fiber extends 
posteriorly (caudad) from the ganglion cell to the end of the 
ganglionic chain ; B, where the fiber runs anteriorly (cephalad) 
from the ganglion cell to the brain; C, where the fiber runs 
