Philosophical Transactions. 137 



Sir Everard pays a merited tribute of praise to the memory of 

 Swammerdam, who was generally remarkably correct in his ob- 

 servations and drawings— he committed one notorious error, that 

 of representing the eyes of the garden-snail to be at the point of 

 the horns ; those organs, on the contrary, are mere feelers, abund- 

 ant in nervous filament, but having no exterior cori'esponding with 

 the cornea of the eye. 



" In all the insect tribe I have examined (says our author,) the 

 brain is formed upon the same general principle, but very different 

 from that of fishes ; the brain is in one mass ; it is too small to 

 admit of a particular description, but contains globules; and from 

 the readiness with which it dissolves upon exposure, there is no 

 doubt of there being a fluid contained in it. Besides this, which 

 is admitted to be the brain of the insect, there is another substance 

 connected to it by means of two chords. This second part has been, 

 I believe, usually called the first ganglion, but when accurately 

 examined it is similar in its texture to the brain ; the two chords 

 which unite them are not properly nerves, since they are upon their 

 first exposure turgid, but soon collapse. These two substances 

 with their uniting chords form a circle, and surround the oesopha- 

 gus ; from the upper mass go off the optic nerves, those to the 

 tentacula, tongue, &c. 



. " From the lower mass go off the nerves to the upper extreme- 

 ties. 



*' I shall therefore consider the upper as the brain, the lower as 

 the medulla spinalis. 



" Below this is a regular line of ganglions, properly so called, 

 being made up of a congeries of nerves, as the ganglions in the 

 human body are now admitted to be. 



" The brain appears to be made up of two lobes. The mass I 

 call medulla spinalis, is also made up of two portions, united toge- 

 ther by the two lateral chords. 



" The ganglions down the body of the animal are united together 

 by a double nerve." — Pp. 5, 6. 



Among insects the humble bee has the largest brain in pro- 

 portion to the size of its body ; it is of a truncated oval form, and 

 gives off the nerves to the eyes and feelers ; its internal structure 

 is made up ol^globules. The substance corresponding in its uses 

 to the medulla spinalis is nodulated on its external surface, and 

 connected with the brain by two long chords, " which differ from 

 nerves in collapsing soon after being exposed." In the moth, ca- 

 terpillar, lobster, and earthworm, the structure of these parts cor- 

 responds with that in the bee. In the garden-snail the brain and 

 rhedulla spinalis are, upon the whole, larger in proportion to the 

 size of the animal than in the bee, " but in this animal there are 

 no ganglions, which may account for those parts being so large." 

 This absence of ganglions in the snail, while they e.\ist in the other 



