460 ME. HUGH SCOTT ON AX 



of the bodv, and liarlng a straight or almost straight coui-se for some distance. The first 

 •pvLi-t of this straight tube has delicate walls (PI. 34. fig. 11. b), often shrivelled in i^repared 

 specimens. The remainder has slightly thicker Avails (fig. 11, c). At the end of the straight 

 tube there is a very curious sharp beud (Pi. 34. figs. 11 d, 16) ; just on the outer side of 

 the l)end the walls of the duct are very slightly invaginated. Beyond the bend the 

 Willis of the duct are thinner again, as in the first poi-tion. Immediately beyond the 

 bend the duct is very narroAT ; it then broadens, and terminates in a slightly swollen 

 cud, the cavity of which is increased by numerous minute rounded diverticula, giving to 

 the end the appearance of a morula (PL 34. figs. 11 f, 15, 16). The portion of the duct 

 fiom the region of the bend to its termination is buried in the interior of a large 

 glandular cell, measuring about 34 ;n across. The substance of this cell consists of a 

 well-defined inner clear portion, which stains very faintly, and an outer granular portion, 

 which stains fairly deeply. The gi'anular part is usually very thin, excej)t in one 

 region remote from the point of entry of the duct and containing the nucleus (PL 34. 

 fig. 16, «). The inner clear part sometimes shows refractive globules (PL 34. fig. 16), 

 more frequently striae radiating from th.e termination of the duct (PL 34. fig. 15, b). 

 How far tliese appearances are aitificial it is impossible to say, but it seems probable 

 that the striae really represent a fibrillar structure of the protoplasm, such as has been 

 di'scribed and figured by Prof. A. Berlese * as existing in the interior or excretory 

 ]jortion of many glandular cells in insects. There is a mass of protoplasm appearing to 

 be of the same consistency as the granular portion of the gland, and containing several 

 rather small nuclei, surrounding the duct at its point of entry into the gland-cell (PL 34. 

 fig. 15, c*). This mass, though in close contact with the gland-cell, is clearly marked oflf 

 from it ; but does not itself, in the sections examined, always show definite division into 

 several small cells, though indications of such division are present. I have endeavoured 

 without success to determine whether these small cells are accessory glandular cells 

 pouring a secretion into the duct at its bend, as might be suspected from the curious 

 conformation of the latter ; but there is no evidence that such is the case. The small 

 cells show no special glandular structure and no division whatever into two portions, as 

 do the large unicellular glands. Traces of a loose capsule of subhypodermal tissue can 

 sometimes be seen surrounding the glands and their ducts. 



The glands of this kind are numerous over the whole dorsal surface in the 

 spaces between the pits of the thread-producing glands, their ducts being shown in 

 fig. 10,/ (PL 34). They are also numerous over areas where the thread-producing 

 glands are almost entirely absent, that is, on the dorsal surface of the tail and 

 the ventral surface of the trunk. They are more sparingly distributed on the ventral 

 surface of the tail. No excretory products have been seen in connection with their 

 orifices, so that it is not possible to state what part they play in the life-history of 

 the insect. 



A third kind of cutaneous glands must be noticed. They are much more localised in 

 their distribution than the preceding, and are confined to the ventral surface. Their 

 pore-plates lie in seven transverse bands in the posterior region of the body, nearthe 



* 'Gli Insetti; vol. i. p. 4C8 .S: fig. 559. 



