288 Is Limulus an Arachnid ? [April, 



the Tracheates, including the Arachnids, in having no tracheae, no 

 spiracles, and no Malpighian tubes. It differs from Arachnids in 

 these characters ; also in having compound eyes, no functional 

 mandibles or maxillae, the legs not terminating, as is generally the 

 case in Tracheates, in a pair of minute claws ; while its brain does 

 not as in Arachnida supply both eyes and first cephalic 

 appendages. On the other hand, Limulus agrees with Crus- 

 tacea in being aquatic and breathing by external gills attached 

 to several pairs of biramous feet; in having a simple brain, which 

 as in some groups of typical Crustacea (Branchiopoda, etc.), does 

 not supply any of the appendages, while the structure of the cir- 

 culatory, digestive and reproductive organs agrees with that of 

 the Crustacea; and, as we have shown in our Embryology of 

 Limulus (this journal for 1870), the development of Limulus is 

 like that of certain other Crustacea with a condensed metamor- 

 phosis, the possession of an amnion being paralleled by that of 

 Apus. In all essential points Limulus is a Crustacean, with some 

 fundamental features in which it departs from the normal Crus- 

 tacean type, and with some superficial characters in which it 

 resembles the scorpion. The importance of these superficial 

 characters Mr. Lankester exaggerates, and upon them with a 

 number of suppositious, a priori, pseudo facts he constructs, by a 

 process quite the reverse of the inductive method, a new classifi- 

 cation of the Arachnida. 



We will now briefly criticise some points insisted upon by Pro- 

 fessor Lankester: and first on p. 510, as regards the ensheathing 

 of the nervous cord by an actual arterial vessel. This is to be met 

 with in a less marked degree in the insects (Lepidoptera) as well as 

 scorpions. As regards the comparison of the nervous system of 

 Limulus with that of the scorpion, the comparison and statement 

 made in our second memoir, which Lankester sets aside, was 

 based on a month's careful study and dissection of the nervous 

 system, particularly the brain of the scorpion, while our author 

 draws his inspiration from Newport's account and figures. The 

 differences between the brain and thoracic ganglionic mass of the 

 scorpion, and that of Limulus are not even correctly stated by 

 our author. The brain of the adult scorpion, as we stated on p. 

 7 of our second memoir, sends off nerves to the simple eyes and 

 to the first pair of appendages ; in Limulus the brain supplies the 

 eyes alone ; the first pair of appendages being supplied from the 



