PSYCHE. 



THE PRIMITIVE NUMBER OF MALPIGHIAN VESSELS IN 



INSECTS.— VII. 



BY WILLIAM MORTON WHEELER, PH.D., CHICAGO, ILL. 



With these conclusions the object of 

 the present paper is attained. As 

 stated in the beginning, the homologies 

 of the Malpighian vessels with other 

 insect or vermian organs are most 

 obscine, and if I venture to add some 

 remarks of a critical nature, it is in the 

 belief that a discussion of the difficulties 

 attending the establishment of such hom- 

 ologies is not without a certain, albeit 

 negative value. 



It is an interesting fact, which has 

 impressed several observers, that the 

 fore-gut, and more especially the hind- 

 gut in many insects, have a very regular 

 hexagonal outline. This is most readily 

 seen in the more primitive orders, like 

 the Orthoptera, where it extends even 

 to the mid-gut which is of entodermal 

 origin. Minot* was struck with this 

 peculiarity while studying Melanoplus. 

 "I cannot but think," he concludes, '"that 

 it (the curious repetition of the number 

 six) will be ultimately found to have 

 some hitherto unsuspected meaning. 

 There are six rows of teeth in the pro- 

 ventriculus, six diverticula arising from 

 the stomach, and twelve longitudinal 



* Histology of the locust (Caloptenus) and the cricket 

 (Anabrus). Second rep. U. S. ent. coram. 1S7S-79 relat- 

 ing to the Rocky Mt. locust. 1SS0. pp. 220-221. 



folds in each diverticulum. There are 

 twelve (twice six) gastroileal folds, 

 arranged in twos, each pair appearing 

 as the double anterior termination of the 

 six ileal folds, which, changing their 

 character, extend backwards through 

 the colon ; finally in the rectum there 

 are six rectal glands." 



The hexagonal symmetry of the hind- 

 gut makes its appearance during embry- 

 onic life, as I have observed in members 

 of the orders Orthoptera, Coleoptera 

 and Lepidoptera. The Malpighian 

 vessels arise at the 6 angles, or horns of 

 the proctodaeal wall. There is evi- 

 dently, therefore, some correlation 

 between the 6 vessels and the hexagonal 

 outline of the hind-gut. 



Miall and Denny * were, I believe, 

 the first to offer an explanation for the 

 hexagonal structure of the rectum. 

 They are of the opinion that "the tend- 

 ency to produce a 6-banded stomodaeum 

 and proctodaeum may possibly be 

 related to the 6 theoretical elements 

 (two tergal, two pleural, two sternal) 

 traceable in the Arthropod exo-skeleton, 

 of which the stomodaeum and procto- 

 daeum are reflected folds." 



* 1. c. p. 126. 



