442 



NATURAL SCIENCE. 



Dec, 



In giving an account of the development of the gill-books of 

 Limulus, Mr. Kingsley refers to Mr. Laurie's views on the relationship 

 of these organs to the lung-book of arachnids,^ and ingeniously shows 

 that the reversal of the faces of the appendage suggested by Mr, 

 Laurie is not necessary. From the embryonic appendage with 

 invagination behind it (Fig. i), can be derived the gills of L?;mf//K (Fig. 2) 

 or the lung of an arachnid (Fig. 3), the folds in the latter case, though 

 on the forward side of the invagination, really corresponding with the 

 hinder surface of the primitive appendage. 



No details of the nervous system are given by Mr. Kingsley, 

 but its development and adult structure have been lately described 



<^^.=^^^^,=:i=^4^^f^=^ 



Fig 3. 



Figs. 1-3. — Diagrams of (i) Primitive Appendages, whicla develop into (2) Gills 

 of Limulus, or (3) Lungs of Arachnid, a — Anterior aspect of animal ; 

 b.s. — Blood-spaces, which are seen to correspond in all three figures. 

 [After Kingsley.] 



by Dr. Patten (4), who shows the correspondence of the embryonic 

 brain of Limulus with that of scorpions, spiders, and insects. He 

 describes a pair of cephalic lobes with three divisions, from which 

 are developed the large " cerebral hemispheres " of the adult. To the 

 ganglia which innervate the chelicerae, the term " mid-brain " is 

 applied ; the five next pairs are called the " hind-brain," and the next 

 pair the " accessory brain." These terms indicate the homologies which 

 Dr. Patten sees between the brain of Limulus and that of the Ver- 

 tebrata, claiming that in the nervous system of the King-Crab fresh 

 support is to be found for his startling theory of the arachnid ancestry 

 of the back-boned animals. The front wall of the cephalic lobes passes 

 downwards into the cavities of a pair of semicircular lobes, identified 

 by Dr. Patten with the infundibulum of the vertebrate brain. From 

 these arise the roots of the nerve of the median eyes, which are com- 

 pared to the pineal eye of vertebrates. Correspondences are also 

 found between the olfactory organs of Limulus and of vertebrates, 

 specially lampreys. Dr. Patten, indeed, states that the nervous 



3 Nat. Sci., vol. i., p. 524. 



