498 Mr, Brayley on the ocular points of the Helicidcej 



And Mr. Guilding himself, probably, when he finds our present 

 knowledge of the subject to be so scanty and so indecisive, may 

 be induced to give it that further attention it so well deserves, 

 and which he appears to be so well qualified to bestow upon it 

 with success. 



Sir Everard Home's Croonian Lecture on the Internal Struc- 

 ture of the Brain, published in the Philosophical Transactions for 

 1824, is illustrated, as most of his communications to the Royal 

 Society have been of late, by a series of engravings from Mr, 

 Bauer's exquisite microscopical drawings. In the present in- 

 stance they represent the structure of the brain in the human 

 subject, and, together with that of the nervous system, in animals 

 of various classes. After considering the minute structure of the 

 brain and nerves as they exist in several groups of the Vertebrata, 

 the author proceeds to point out the peculiarities of those organs 

 in Insects and Worms ; and whilst thus treading upon the same 

 ground on which Swamm^rdam preceded him, he awards a just 

 tribute of praise to that great man, who, in many instances, has 

 left nothing for those who follow him, but to bear testimony 

 to the correctness of his representations and judgment. '' There 

 are some points however," Sir Everard observes, " in which he 

 gave way to public opinion, and did not disbelieve what every 

 one said must be true. I allude to his attempt to represent the 

 eye of the Garden Snail at the point of the horn, which does not 

 exist. He found black rete mucosura, which he mistook for 

 , nigrum pigmentum, and a pellucid part which he took for cornea. 

 To shew this fallacy, I have annexed Mr. Bauer's representation 

 of these parts. Swammerdam has given a faithful representation 

 of the nerve, which might have undeceived him, it having no 

 resemblance to other optic nerves, but being like those commonly 

 met with going to tentacuia." Accordingly, two figures by Mr. 

 Bauer are given from the Garden Snail, both of which are in part 

 copied in Plate xvii. On the first of these (fig. 3.) shewing the 

 brain and nerves, as magnified four diameters, Sir Everard makes 

 the following remarks : 



" In this animal the brain is made up of two apparently equal 

 portions. As the appearance at the termination of the two large 



