432 



Projecting into the rectum from its anterior wall is a 

 single pair of rectal glands (figs. 22, 164). Each is some- 

 what pyramidal in shape, and presents an outer syncytial 

 region, covering an inner medullary region in which cell 

 boundaries are sometimes just visible. The development of 

 the organ, which will be considered later, shows that the outer 

 cortex is merely the fused outer ends of the large cells which 

 form the medulla and which sometimes lose their individuality. 

 Nuclei do not, therefore, occur in the outer zone, but it€ 

 distinctness, especially in immature stages, is very obvious. 

 The cytoplasm of the cells is granular. The nuclei are large 

 and granular and have a gigantic nucleolus. At the base of 

 the pyramidal mass is a cavity, which is continued as a narrow 

 duct upwards through the whole organ. The cavity does not 

 appear to open into the body cavity; on the contrary, below 

 it the lining of the rectum undergoes a special chitinisation. 

 Through this chitin piece passes a large tracheole, which runs 

 through into the rectal gland and there terminates. At the 

 base of the pyramid are a number of curious cells ; each is a 

 hair-like filament, with a nuclear thickening either at its base 

 or elsewhere along it, and these filaments stretch from one 

 side right across the basal cavity towards the other (figs. 164, 

 165). 



What the function of these extraordinary organs is I 

 am quite unable to say. Lowne, searching for excretory 

 organs in Calliphora, after denying the excretory function of 

 the malpighian tubules, ascribed this function, without any 

 definite reason, to the rectal glands. Hewitt observed them in 

 the house-fly undergoing rhythmical contractions ; in that 

 insect they communicate with the body cavity, and he likewise 

 concluded that they were excretory organs. The only fact in 

 favour of this view, however, is their curious position ; but 

 the development oif such organs in an insect already well pro- 

 vided with excretory tubules, seems to contradict this view. 

 In Nasoma the only communication with the body cavity that 

 they may have is by means of the basal filamentous cells; 

 but what their function is must remain, for the time, un- 

 decided. In most insects two pairs of rectal glands seem to 

 be present. 



CThe single salivary gland is composed of a relatively small 

 number of thickened granular cells, with large granular 

 nuclei. A few cells in the centre of the gland have a vacuo- 

 lated or branched appearance, giving the interior of the gland 

 a spongy structure. The gland lies in close contact with the 

 great salivary duct, and the walls of this duct, in the neigh- 

 bourhood of the gland, present the same vacuolated appear- 

 ance as characterises the interior of the gland. The gland 



