658 MEDICAL ENTOMOLOGY 



the central sac is smaller and has a single posterior diverticulum (Plate 

 LXXXIII, fig. 5), which is often split at its extremity into two short 

 branches ; it always contains a white fluid the excretion of the 

 Malpighian tubes. 



In Margaropus and Hyalotnma the rectum consists of a single sac 

 (Plate LXXXIV, figs. 1, 2, 4 and 5) lying in the same situation as that 

 of Argas and Ornithodorus ; like that of the latter it contains a white 

 fluid. 



On reflecting the dorsal integument the Malpighian tubes are seen 

 for a short part of their course lying over the mid-intestine ; they will be 



recognized by their yellowish white colour and by the 

 The Malpighian tubes 



ract that when punctured a thick chalky substance 



oozes out. Each tube begins blindly in the anterior part of the body 

 in the neighbourhood of the antero-lateral diverticulum. From this 

 point it passes outwards below the salivary gland, around the free end of 

 which it may coil more than once. It then comes into contact with the 

 main tracheal trunks as they leave the spiracle, from which it receives 

 a liberal supply of tracheal twigs, and, turning inwards, makes several 

 coils round the branches of the antero-lateral diverticulum. It next 

 passes upwards and coils round the oviduct and the upper part of the 

 ovary, and on reaching the dorsal surface comes into close relationship 

 with the mid-intestine and the dorsal blood vessel ; here it may make 

 one or several turns round the mid-intestine. It then passes backwards 

 and dips down towards the ventral surface, forming a number of 

 convolutions in the posterior part of the body, where it comes into direct 

 contact with almost all the posterior diverticula and the ovary. Finally 

 it enters the rectum on its ventral surface by an opening close to that of 

 its fellow of the opposite side. 



Owing to the great length of the Malpighian tubes and to their compli- 

 cated course they come into close relationship with almost every organ, 

 and more particularly with the intestinal canal and its diverticula, around 

 which they coil in several places. From this it can be readily under- 

 stood that a motile parasite, such as a spirochaete, may easily pass 

 into the tubes either from the haematocoele or from the intestinal canal. 

 It should be noted also that the tubes exhibit great functional activity ; 

 during the period of oviposition they are loaded with secretion, and 

 can be seen through the dorsal integument as broad yellowish white 

 bands. 



In order to study the anterior part of the alimentary tract, the antero- 

 lateral and antero-median diverticula should be cut off close to the 



