May 1S93.] 



PSYCHE. 



457 



tinctly separated from the seventh than are 

 the other segments from each other, without 

 hairs, but armed with two pairs of terminal 

 hooks; the upper or anterior pair blunt 

 spine-like, approximated and stout at base, 

 somewhat appressed but not terminally 

 recurvate or hooked; the lower or inferior 

 pair more removed, terminally recurved 

 below, sharp claw-shaped, slightly divergent, 

 directed inferiorly ; anterior to the latter on 

 ventral surface there is a pair of small tuber- 

 cles. Ten pairs of stigmata or spiracles, as 

 follows : Prothoracic spiracle on side at 

 anterior margin of prothorax ; mesothoracic 

 spiracle on anterior border of wing bases; 

 metathoracic spiracle in the anterior lateral 

 angle of dorsum of scutellar segment; and 



an abdominal spiracle in the anterior lateral 

 corner of dorsum of each of the abdominal 

 segments 1 to 6, the 7th segment having a 

 small median lateral one higher up on side of 

 dorsum; the spiracles (except the mesotho- 

 racic) appear as a corneous circle marked by 

 radiating lines within, those on the 7th 

 segment showing this structure less dis- 

 tinctly, while the mesothoracic spiracle is 

 indistinct and does not usually reveal this 

 structure at all. 



Length, 8.5 mm. (including cephalic 

 horns) ; width of basal abdominal segments, 

 2.25 mm.; length of long filament-like hairs 

 of 3d to 5th segments about 3 mm., those of 

 1st and 2d segments over 4 mm. 



THE PRIMITIVE NUMBER OF MALPIGHIAN VESSELS IN 



INSECTS.— I. 



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



Since the days of Schwammerdam 

 anatomists have most naturally evinced 

 far greater interest in the physiology 

 than in the morphology of the Malpig- 

 hian vessels. Hence we are in posses- 

 sion of a much larger body of facts beai - - 

 ing on the function than on the 

 phylogenetic history of these interesting 

 organs. Their possible relations on 

 the one hand to the trachea?, which 

 have a somewhat similar orgin, and on 

 the other to vermian nephridia, which 

 have a similar function, are still 

 shrouded in the deepest obscurity. 

 Before these fundamental questions 

 can be answered satisfactorily, it will be 

 necessary, I believe, to come to some 

 definite conclusion in regard to several 

 minor questions. Foremost among 



these is the question as to the primitive 

 number and arrangement of the organs 

 under consideration. 



No fact in insect development is 

 better authenicated than the derivation 

 of the Malpighian vessels. It was 

 Biitschli* who in 1870 first showed that 

 in the bee the paired excretory organs 

 arise as hollow diverticula of the hind- 

 gut which itself arises as a more exten- 

 sive invagination of the ectoderm at 

 the caudal end of the embryo. All 

 succeeding writers have confirmed this 

 observation. 



It is worthy of note that there is ex- 

 tensive variation in the time at which 

 the vessels make their appearance in 



*Zur entwicklungsgeschichte der biene. Zeitschr. f. 

 wiss. zool. 20. bd. 1S70, p. 541. 



