passage between the two for the 

 !.; h segment of the thorax contains a ganglion, 

 the meta-thoracic one, which gives nerves to 

 the wings, being the largest. In the abdominal 

 portion of the cord, which extends as far as 

 the penultimate segment, there are six double 

 ganglia very distinct from each other. Tins is 

 exactly the number found by us in the same 

 portion of cord in the Carabidtt, although, 

 according to Uurmeister, there are only five. 

 Thus, then, in the Vurjiculida, in which there 

 is the most extensive motion of the segments 

 of the abdomen, there is the same number of 

 ganglia as in the Carabulie, in which most 

 of the abdominal segments are anchylosed 

 together and immovable, as in the Lamclli- 

 cornes, in which the whole of the cord is 

 situated within the region of the thorax. In 

 the oil-beetles, as in Proscarabaus vulgaris, 

 there are as usual three thoracic ganglia, the 

 largest being the meta-thoracic, although the 

 proper wings, and scarcely even the elytra, do not 

 exist. In the abdominal region there are five 

 ganglia, but smaller than those of the thorax, 

 although it is stated by Uurmeister* that these 

 ganglia of the thorax are larger than those of 

 the abdomen when perfect organs of flight are 

 developed, but smaller when they are absent. 

 So far as our own observations have extended, 

 we have invariably found the thoracic ganglia 

 larger than the abdominal, whether organs 

 of flight exist or not, a condition that might 

 naturally be expected whether the ganglia be 

 connected with the production of nervous energy 

 in the parts, or be only the centres of sensation. 

 In the full-grown larva of this insect, of which 

 we have examined a considerable number, but 

 which at present appears to be scarcely if at all 

 known to naturalists, we have found twelve per- 

 fectly distinct sub-oesophageal ganglia. Of these 

 the fifth was the largest and separated from the 

 fourth only by a very short cora, as were also 

 the eleventh and twelfth, besides which the 

 twelfth was larger than the eleventh, and ap- 

 peared as if formed at an early period of two 

 approximated ganglia. That in the earliest 

 state of this insect there are thirteen sub- 

 oesophageal ganglia seems highly probable. On 

 watching the changes that take place it is found 

 that this double terminal ganglion becomes united 

 to the eleventh, and that a similar union takes 

 place between the fourth, fifth, and sixth, so 

 that only five separate abdominal ganglia exist 

 in the perfect insect. In the Forficula, which 

 does not undergo a perfect metamorphosis, a 

 similar change appears to lake place at a much 

 earlier period, the terminal ganglion being dis- 

 tinctly formed of two masses, and the ganglion 

 of the meta-thorax or "ini:-bearing segment of 

 three. A similar change appears also to occur 

 in the Stapltylmidf. In (.'nn/i/iiliix Hi//n7/oM 

 (Jig. 341), in which the abdominal segments are 

 as freely moveable as in the Earwig, but which 

 undergoes a more complete metamorphosis, 

 there are nine sub-cesophageal ganglia, only 

 the last three of which are abdominal, ihr la^t 

 five segments being entirely without ganglia. 



* Op. ciu p. 281. 



INSECTA. 



There is exactly the same form and position of 

 the nervous system in tin; common s|>ccies, 

 (lull-ins uli-ni. On compani icum- 



stances it is found that a much smaller i. 



ulia in general exists in tln>~. 

 insects which have undergone a complete mela- 

 morphosis than in the larva stale, and than in 

 ihuM -that scarcely change tlieir form. In the 

 Gryllide, Acrida viridissima (Jig. 4 10), there is 



Fig. 410. 



Ntnmu lyitem of Acrida riridioima. 

 A, brain ; 1), antenna: ; B, oplic nerves ; d, man- 

 dibular nerve ; e, auxiliary connecting nerve ; 

 y, nerve of prothoracic legs ; i, of second pair 

 of legs ; A, third pair ; n, tendon of flexor mus- 

 cle with its nerve accompanying it to it insertion 

 at extremity of the femur; c, second head of the 

 same flexor muscle at the end of the tibia. 



the same number of ganglia as in the Forficula, 

 and a similar difference in the size of the 

 thoracic ganglia. But in this insect there is 

 aKn a rloMT lati nil approximation of the abdo- 

 minal cords, and a comparatively small 

 and more elongated form of their ganglia, 

 evidently shewing a tendency to a more con- 



