414 THE ALIMENTARY CANAL OF THE IMAGO. 



then endeavour to state as briefly as possible the other view 

 of their nature. 



(1) ' They are developed from the proctodeum.' This state- 

 ment is usually regarded as correct. I will only observe here 

 that in both the embryo and the nymph the Malpighian tubules 

 communicate with the mesenteron and not with the procto- 

 deum. 



Graber, although he holds the view that they are developed 

 from the proctodeum, figures them in an early embryo opening 

 into the mesenteron [114, Taf. III., Fig. 27], and according to 

 my observations his figure is correct. 



The statement that ' they open into the rectum ' is incorrect. 

 In nearly every insect they open into the pyloric or distal 

 extremity of the chyle stomach or into the commencement of 

 the proximal intestine. In the Blow-fly larva there are 35 mm. 

 of intestine between the anus and the Malpighian ducts, and 

 in the imago 6 mm. When the statement has been made, the 

 authors who have made and accepted it had probably only 

 those insects in mind like the Cockroach in which the distal 

 intestine is very short. 



(2) ' They appear at a very early period of development.' 

 So do the liver tubules of the vertebrate. Remak says ' They 

 appear in the embryo chick later than the rudiment of the 

 ^'olffian duct, but before the first Wolflian tubules.' 



(3) ' They agree anatomically and histologically with urinary 

 tubules.' 



As diverticula of the intestine high up in its course, they 

 certainly resemble a tubular hepato-pancreas rather than a 

 kidney. The cells are large, contain fat and pigment, and 

 undergo partial disintegration at least during secretion. All 

 these characters point to a hepato-pancreas rather than a 

 kidney. 



(4) ' They contain crystals of uric acid.' 



I have examined many hundreds of sections of Malpighian 

 tubules, and I never yet saw any crystals in them except of 

 artificial origin. In imperfect preparations numerous crystals 

 arc liable to form in the fat bodies, alimentary canal and blood. 



