290 Is Limulus an Arachnid ? [April, 



the carapace may " be considered as representing six coalesced 

 tergites." Partly on metaphysical grounds, and partly from the 

 presence of moveable spines on the sides, which, however, are 

 situated on the anterior limb-bearing segments of the abdomen, as 

 well as on the 7th and 8th limbless segments, our author is en- 

 couraged in the belief that these four hypothetical segments really 

 exist. We prefer the plain teachings of observed facts, which are 

 capable of demonstration and proof, and would ask for better evi- 

 dence than this article affords of the existence of such segments. 

 We would also continue to regard the anal spine as the telson. 

 Lankester's " telson" is made up of the consolidated thirteenth 

 and fourteenth segments of the body plus the anal spine or fif- 

 teenth (or ninth abdominal) segment. 



Our author sets out with the foregone conclusion that he 

 " must " find in the " abdominal carapace " of Limulus the rep- 

 resentatives of the twelve abdominal segments of the scorpion, 

 and so with a method of his own he creates them out of his inner 



In like manner he feels compelled to offer a new interpretation 

 of the scattered, individual, simple eyes of the scorpion, and at- 

 tempts to show that after all they are compound eyes like those 

 of Limulus, with the difference that in Scorpio they are " in a less 

 compact form." Now the compound eye of Limulus, like that of 

 the lobster or any other Crustacean or insect, possesses a common 

 basally undivided retina, in Limulus a common undivided outer 

 cornea, while the two simple eyes in Limulus have each a sepa- 

 rate cornea, a separate retina, and each ocellus is supplied by a 

 separate nerve arising independently from the brain. 



In like manner our author labors to diminish the importance of 

 the differences between the cephalothoracic appendages of the 

 Arachnida and those of Limulus. 



Professor Lankester then ventures, we think, somewhat hastily, 

 to homologize the first pair of abdominal appendages of Limulus 

 with a little triangular median sternite in the scorpion. Then he 

 fancifully homologizes the comb-like organs of the scorpion with 

 the second pair of abdominal legs of Limulus, and also homolo- 

 gizes the respiratory lamellae with the " lamelliform teeth of the 

 scorpion's comb-like organs." The author farther seriously at- 

 tempts to homologize the four pairs of stigmata of the scorpion 

 with the four last pairs of biramous respiratory feet of Limulus. 



