664 MEDICAL ENTOMOLOGY 



periphery of the cells. The cells now begin to absorb the dark globules 

 from the digested blood until they become completely filled. The 

 globules become transformed into clear drops. In a suitable prepara- 

 tion the absorption of the globules from the blood and their transforma- 

 tion into clear droplets may be seen going on at the same time. 

 The cells now project more and more into the lumen until they remain 

 attached to the basement membrane only by a slender stalk ; many 

 of them become free in the lumen of the gut and their places are taken 

 by fresh cells which have grown out of the small cells near the basement 

 membrane. As absorption proceeds the clear globules become trans- 

 formed into the yellow balls which are seen in the fresh condition in a 

 tick recently changed from the nymphal stage to the adult. When all 

 the blood has been absorbed the delicate intima lining the cells becomes 

 detached and lies free in the gut ; Samson compares it to the peritrophic 

 membrane of the mid-gut of insects. It is interesting to note that 

 Nuttall and Strickland have found that the intestine of Argas persicus 

 contains an anticoagulin but no haemolysin. 



The salivary glands lie in an oblique position on each side over the 



bases of the first three legs, and can be recognized by their characteristic 



appearance, very like that of a bunch of grapes in 



Salivary glands and m i nature- At its anterior end each gland comes into 

 ducts : Plates LXXXIII & 



and LXXXIV contact with the base or the mandible or its side and 



externally with the coxal gland ; the posterior or free 

 end lies over the main tracheal trunks. Each gland consists of a number 

 of lobules, made up of globular acini arranged about the central excretory 

 duct ; in addition there are a number of single-celled glands on the main 

 duct and some of its larger branches. Each acinus is made up of two 

 kinds of cells ; one kind is situated at the opening of the acinus and the 

 other at the base, and therefore spoken of as the ' fundus cells '. Both 

 in starving and in fed ticks the cells at the mouth of the acinus contain 

 large granules which stain deeply with haematoxylin. The fundus cells, 

 on the other hand, have only a few granules in starving ticks, while in 

 fed specimens they are often completely filled with clear globules of 

 excretion, which stain only feebly with haematoxylin. The duct of the 

 acinus begins as a narrow channel, soon developing into a definite duct 

 lined by flat cells ; it joins similar ducts to form a lobular duct which 

 in turn receives other lobular ducts and then enters the main channel; 

 in this way an arborescent appearance is produced. 



The large single-celled glands consist of pyramidal cells with broad 

 .bases; their protoplasm consists of a peripheral zone and a middle zone, 



