No. 2.] THE EMBRYOLOGY OF LIMULUS. 245 



On the other hand, we must not lose sight of the fact that 

 numerous observers have recorded a biramous condition in the 

 appendages of various " Tracheates." Among others we would 

 mention the biramous pedipalps in Dendryphantes recorded by 

 Croneberg ('80), the biflagellate antenna of an Indian Lepisma, 

 and of an embryo Blattajavanica by Wood Mason ('79), the 

 bifid condition of the antenna of Blatta by Wheeler ('89), while 

 Patten ('84), in the same form describes the maxillae and labium 

 as " formed respectively of two and three branches, the second 

 maxilla thus attaining the typical trichotomous structure of the 

 Crustacean appendages." Neither must we forget the peculiar 

 antennse of the Pauropida in this connection. 



The so-called Malpighian tubes (point 3.) have a far dif- 

 ferent bearing upon the classification of the Arthropods from 

 that which they were supposed to have a few years ago. In 

 fact, two entirely different structures have been included under 

 the one name, and the existence of excretory tubules in both 

 Hexapods and Arachnids, instead of proving the close relation- 

 ship of the two groups, is, in view of our present knowledge,, 

 an argument against it. In the Hexapods these organs have 

 been shown by numerous observers to be of proctodeal, and,, 

 therefore, of ectodermal origin. In the Arachnida the supposed 

 homologous organs, to which the same name has been given, 

 are, in all probability, outgrowths from the mesenteron, and 

 hence entodermal. This has been shown by Loman ('86-7) for 

 both the tetra- and the dipneumonous Araneina, and by Laurie 

 ('90) for the scorpion.i Hence these organs, — ectodermal in 

 the one group, entodermal in the other — instead of indicating 

 community of descent for Arachnids and Hexapods, must rather 

 be regarded as indicating that the group Tracheata as usually 

 limited is polyphyletic in origin. 



1 Kishenouye ('90) claims that in the Araneina both the Malpighian tubules and 

 the stercoral pocket are derivatives of the mesoderm, the cavity of the latter being^ 

 the coelom of that region of the body. This is on its face improbable. It would 

 seem that the failure of many investigators to recognize that these tubules 

 are entodermal in origin was due to the fact that since they were known to be 

 ectodermal in the Hexapods, they have been used as regional tests, the fact that 

 they arose from a certain part of the alimentary canal being sufficient reason for 

 regarding that portion as proctodeal. Beddard's view ('89) that the Malpighian 

 tubes are derived from nephridia secures no support in the Arachnida. 



