978 THE AMERICAN NATURALIST.  [VOL. XXXIIL 
fibres derived from the ventral horn cells of the cord and distributed 
to the striated body musculature; (2) somatic sensory or general 
cutaneous fibres terminating in the dorsal horn and supplying the 
skin of the body; (3) visceral motor fibres supposed to pass from 
the lateral horn outward by both dorsal and lateral roots; and (4) 
visceral sensory fibres passing in through the dorsal roots only. 
In the cranial nerves, in addition to these four components, a fifth, 
the acustico-lateral, can be distinguished in connection with the ear 
and lateral line organs. No cranial nerve contains all these com- 
ponents, and there is an obvious tendency towards the concentration 
of the fibres of each component, so as to form a single system with a 
common center in the medulla. 
The composition of the various cranial nerves is as follows. The 
hypoglossal is composed of somatic motor fibres and passes out as 
the first member of the first spinal complex. The spinal accessory 
is made up of visceral motor fibres and passes out with the vagus to 
innervate the trapezius muscle. The vagus is in the main formed 
of visceral motor and visceral sensory fibres, together with a few 
somatic sensory and acustico-lateral fibres. The glossopharyngeal 
contains only visceral motor and visceral sensory fibres. The audi- 
tory is exclusively acustico-lateral. The facial is composed of vis- 
ceral motor, visceral sensory, and acustico-lateral fibres. The ab- 
ducens is wholly somatic motor. The trigeminal is visceral motor 
and somatic sensory. The trochlear and oculomotor are both 
somatic motor. The optic and olfactory nerves have not as yet 
been placed in any category. GHP 
Reactions of Entomostraca to Light. — R. M. Yerkes! has studied 
the reactions of two entomostracans, Simocephalus and Cyclops, to 
differences in light intensity, photopathy. In the experiments the 
influence of the direction of the light was eliminated and the animals 
were subjected to light of graduated intensity. Simocephalus moved 
into regions of greater intensity of light, że., was positively `photo- 
pathic; and the amount of positive movement varied, within certain 
limits, directly with the intensity of the light. Diffuse daylight 
caused a greater positive response than direct sunlight. Cyclops 
proved to be not photopathic. It was also shown that Simocephalus 
preferred the orange and yellow portion of the spectrum of illumi- 
nating gas, but the author concludes that this is a response to inten- 
1 Yerkes, R. M. Reactions of Entomostraca to Stimulation by Light, Amer. 
-~ Journ. Physiol, vol. iii, pp. 1 57-182. November, 1899. 
