274 ANATOMY. 



tension towards the orbit very distinct ; in Locust a the cerebrum is 

 smaller than the optic nerve, which springs from it with a very narrow 

 base, but which then very suddenly widens into a cone ; this is pre- 

 cisely the case also in the Libellulce and flies which possess large eyes 

 and a small skull, and in which the optic nerve of one eye is generally 

 much larger than the entire cerebral ganglion. When arrived in the 

 orbit it radiates into many branches, as we shall describe more fully 

 below, in the detailed description of the eye. The auxiliary optic 

 nerves (nervi opticisecundariij, which are peculiar to such insects only 

 that possess stemmata, originate from the central portion of the 

 cerebrum, and extend as simple and very thin filaments to the spot 

 where the stemmata are situated, and gradually diverge from each 

 other. Thus each eye receives a distinct nerve, but which with its 

 colleagues originate from one portion of the brain. It is well known 

 that all the larvae of insects with an imperfect metamorphosis possess 

 merely stemmata, which are placed where subsequently in the perfect 

 insect the large reticulated eyes are found. The nerves of these stem- 

 mata spring from the lappet-shaped distension of the cerebrum, some- 

 times separated (Calo.ioma, PI. XXXII. f. 1), sometimes united at 

 the base (caterpillars of the Lepidoptera), and run, each singly, to an 

 eye. In Vespa the nerves of the stemmata have a common stem (PI. 

 XXXII. f. 7-) ; in the bees they sit upon short clavate projections of 

 the cerebrum, and a distinct nerve does not seem to originate from 

 these knobs *. In the neuter bees we find close to these large knobs 

 two other small ones on each side, but which do not rise to the stem- 

 mata. 



Besides these two main branches no other true nerves of the senses 

 originate from the cerebrum ; we observe merely smaller ramifications, 

 which give off branches partly to the muscles and partly form filaments 

 connected with the nerves of the cerebrum, and lastly, they may be 

 partly considered as the commencement of the nervus sympathicus. 

 But as below we shall devote our attention to this last system we will 

 reserve our investigation of its origin from the nerves of the cerebrum 

 until then. 



The cords which connect the cerebrum with the cerebellum originate 

 from the lower or deeper portion of the ganglion, as the nerves of the 

 antennae do from the anterior or superior portion, and after the optic 



' Treviv.'imis, Biologic, vol. v. PI. II. f. 1 .3. r, r. 



