APPEND IX VIII. 
YERSIN'S RESEARCHES ON THE FUNCTIONS OF THE NERV- 
OUS SYSTEM OF THE ARTICULATE ANIMALS. 
[Compare with chapter XI on the Brain of the Locust.] 
In our chapter cm the Brain of the Locust we omitted to record Yersin's* opinions as 
to the functions of the nervous system of crickets. Wo translate from II. de Saussure's 
"Notice sur la Vie et les Ecrits de Alexandre Yersin," 186(5, the following' abstract of 
his researches on this subject. 
The author followed two different methods in his researches; first, l>y making sec- 
tions of the nervous chain ; second, by endeavoring to isolate the ganglia. 
The results attained by means of sections were quite varied. In performing on some 
crickets the section of the two nervous cords in the head, between the supra-cesopli- 
ageal and infra-oesophageal ganglia, there resulted as a consequence of this operation 
a series of physiological phenomena. After a moment of stupor, the insect rose on the 
extremities of its feet while carrying its head directed forwards. Then the cricket 
turned in a circle to the right, while rubbing its head with the left foot, or vice versa. 
When the section of the two commissural cords is performed between the head and 
the thorax, as, for example, wheu we decapitate a Blatta, the insect can still live ten 
or twelve days ; the body continues to bend itself in such a way as to carry the poste- 
rior feet towards the head, which is wanting, as if to clean them with the mandibles. 
When the insect thus mutilated is excited it endeavors rather to defend itself than to 
escape, as an uninjured individual would. If the section is performed on crickets be- 
tween the second cephalic ganglion and the first thoracic, without decapitation, it 
will be found that wo have isolated the community of action in the head and body, 
which move independently of each other ; the animal constantly tries to extend its feet 
as if to clean them with the mandibles, but the maxilhe do not recognize them. These 
are almost the only movements which the insect makes. Exposure to the sun reani- 
mates it, and it leaps about a little ; forty days after the operation it sometimes becomes 
euddeuly aroused from its torpor. The act of coupling can be performed, even with 
a female operated upon, but the latter is incapable of laying eggs. The insect still 
eats a little, but while only the head eats, the trunk does not perceive it, and continues 
to extend the feet towards the mouth as if to rub them ; so that the head eats, without 
perceiving the fact, its own feet as well as the food; the mutilation of the feet causes 
the insect to tumble about, which seems to prove the presence of pain. The reflex 
movements are very easy to provoke in this particular case, and tUj voluntary move- 
ments either of tho trunk or of the head are exercised with a remarkable facility, 
although in an independent way. Thus the insect is capable of leaping ; if it is stim- 
ulated too long it gives some symptoms of anger; if it is placed on its back it promptly 
turns over. The crickets operated upon live as long as those which are uninjured. 
In making two sections of the cords of the ganglionic chain, so as to completely 
isolate one of the ganglia, we likewise isolate the functions of the nerves which aro 
distributed from this ganglion, but without interrupting them. The reflex actions 
become iu this case very pronounced. They are always of long duration ; for exam- 
ple, when we excite the valves of the ovipositor, they continue to open and shut per- 
sistently; in exciting a foot belonging to the third pairweobtain an immediate reflex 
action on the one corresponding to it. The feet of the second pair seem, however, to 
be an exception to the rule, and only react with great difficulty on each other. If we 
isolate several ganglia collectively from the rest of the chain, we obtain analogous and 
naturally more varied reflex actions. 
Yersin followed up his experiments by afterwards producing some lesions in the 
'Alexander Yersin was a Swiss naturalist, who wrote several important and fruitful essays on the 
haliits and physiology of tho locusts and crickets. His essay on the nervous system of insects was the 
following: Kecherches sur les fonctionsdu systemenerveux dans les aniinaux'articules. Societ6 Vau. 
dois des Sciences Naturelles, et Acadeuiie des Sciences de Paris, 185U-'57. 
[73] 
