392 Annals Entomological Society of America [Vol. IX, 



THE MALPIGHIAN VESSELS. 



From a morphological point of view, the Malpighian vessels 

 of an insect are ectodermal structures, which arise during 

 embryonic life as evaginations of the distal end of the hind- 

 intestine (which is itself an invagination of the ectoderm). 

 In a typical insect, the Malpighian vessels empty into the 

 alimentary canal at the junction of the mid-intestine with the 

 hind-intestine, and after a greater or less course end blindly 

 in the body cavity. 



In the larva of Haltica bimarginata the arrangement is very 

 characteristic and presents some interesting and rather unusual 

 features. In this insect there are six Malpighian vessels, 

 which are morphologically divisible into two series, differing 

 from one another in point of origin, in length, in macroscopic 

 aspect, and in microscopic structure. 



Such a dimorphism in the tubes of the same individual is 

 by no means confined to Haltica, but has already been reported 

 for numerous Coleoptera. Indeed, much greater dimorphism 

 has been described for many insects, and while most of the 

 instances cited have been discredited by later workers, it is 

 generally admitted that there is a very decided dimorphism, 

 correlated with a difference in function, in the Malpighian 

 vesseis of Stratiomyia (Vaney, 1900) and of phasmids (Sinety, 

 1900). 



In Haltica, the first series is composed of four vessels which 

 unite at their bases, forming what is generally termed, from 

 analogy with the vertebrates, an urinary bladder. This small 

 ovoid bladder empties directly into the hind intestine, shortly 

 behind its union with the mesenteron. (This condition is 

 illustrated in Figures 1 and 5). At the point of junction 

 of the mid-intestine and the hind-intestine there is a sharp 

 bend, and between the mesenteron which runs caudad and the 

 ileum which extends cephalad, is formed a strong angle, on the 

 inner side of which the bladder opens directly into the lumen of 

 the intestine. 



The four vessels leave this bladder in a parallel series so 

 that there are two outer vessels and two inner. These tubes, 

 which are more or less imbedded in the adipose tissue, are 

 long and somewhat twisted, so that it is difficult to trace their 

 cours2. especially as they are easily broken. They are closely 



