THE SALIVARY PUMP 517 



The tubular salivary glands (Plate LXIV, fig. 2), described by Landois, 

 lie in the neighbourhood of the cardiac glands. Each consists of a fine 

 tube bent upon itself, the wall being formed of a single layer of small 

 cells with some muscular tissue. According to their discoverer they are 

 best recognized by their rythmical contractions. They are said to open 

 into the commencement of the crop. The branched salivary gland of 

 Landois (fig. 3) is even more minute and difficult to find than the 

 preceding. It consists of short branched tubules arising from a common 

 stem, which opens into the oesophagus.* 



Landois suggested that the secretion of the salivary glands passes 

 partly into the wound at the time of feeding, and partly into the aliment- 

 ary tract during the intervals. This is not in accordance with what 

 one finds in other blood-sucking insects. Possibly those glands which 

 open into the alimentary tract posterior to the mouth have some function 

 other than the elaboration of saliva. 



The salivary pump or valve (Plate LXIV, fig. 4) bears a striking 

 resemblance to that which has been described in the mosquito. It 



lies anterior and ventral to the pharynx, and is at- 



... i 11 , The salivary pump 



tacned to the ventral wall and the supporting arch 



of the membraneous chamber which has been referred to as the buccal 

 cavity. It consists of a spindle-shaped or vase-like cup of chitin, 

 somewhat elongated in front, and with its narrow end directed to 

 the point at. which the two mandibles come in contact with one another. 

 The broad posterior end is closed in by a membrane, in the middle of 

 which there is inserted a short rod of chitin, which passes upwards 

 a little distance below the ventral wall of the pharynx. A number 

 of bands of muscles fibre pass obliquely from the ventral surface of 

 the pharynx to the rod, contraction of these pulling the rod, and 

 therefore the membrane, away from the cup, and thus creating a 

 negative pressure within its cavity. The salivary duct, formed by 

 the union of the ducts of the two sides^ opens into the middle of 

 the ventral surface of the cup, and the negative pressure will therefore 

 result in drawing the saliva from the glands into the pump. The ducts 

 are lined throughout with a ringed chitinous intima like that of a 

 trachea, which will effectually prevent occlusion. Presumably there 

 is some valve which prevents ingress of blood into the pump when 

 it is in action. The passage of the saliva from the pump is best 

 accounted for, as suggested by Nuttall and Shipley in the case of 



*, Neither of these glands has been seen. by the writers. 



