ABEEEANT FORM OF COCCID.E. 459 



potash. On the tail they are very scantily distributed, and only the smaller ones are 

 present. On the ventral surface of the insect they are almost absent ; there arc a few 

 small pairs arranged more or less definitely on each of the segments of the posterior 

 region, and a small pair on each anal lobe. 



Under each pore-plate is a single large glandular cell (PI. 34. fig. 17, a), about 48 /i 

 across in a direction parallel to the surface of the body. The two cells under each pair 

 of i^ore-plates lie touching one another, and their contiguous sides are flattened. In 

 transverse sections each jonir may tlius appear to be a bicellular gland. But each cell 

 has its own pore-plate and secretes its own thread, for two separate threads emerge from ^ 



each of the pits in the integument (PL 34. fig. 14) ; therefore each pair of cells must be 

 looked upon as consisting of two unicellular glands in close proximity to one another. 



The substance of each of these glandular cells is divided into two portions. Imme- 

 diately under the pore-plate is a small well-defined part, much clearer and less deeply 

 staining than the rest. The remainder of the cell, which contains a large oval nucleus, 

 is much less clear and stains fairly deeply ; this part has, in sections stained with 

 hsematoxylin and orange G, the peculiarity, which it shares with the chitinous cuticle, 

 of taking up the latter stain, whereas its nucleus and the adjacent hypodermal and 

 subhypodermal tissues take up the hsematoxyHn. The arrangement of these pits and 

 glands with respect to the said hypodermis is worth noting. Beneath the hypodermis is 

 a loose layer of subhypodermal cells (PL 34. fig. 17, e). Tiie hypodermal layer is inter- 

 rupted by the invagination of the chitinous cuticle to form the walls of the pit, and 

 beneath tlie floor of the pit is represented only by the two glandular cells. On the other 

 hand, the subhypodermal layer, at the point where it abuts against the walls of the pit, 

 is invaginated so that it forms a loose capsule ensheathing the pair of glandular cells 

 (PL 34. fig. 17,/). 



On the dorsal surface of the tail, beyond the area of the pairs of pore-plates described 

 above, and in the region of the fourth segment, there are two groups of curious structures, 

 one on either side of the middle line. They are pits in the integument, and when seen 

 in side view are like hollow inverted cones with obtuse and rounded apices (PL 34. 

 fig. 10, d). They vary in shape, size, and arrangement. They are usually, but not 

 always, in pairs ; their number varies in different individuals, and is not even always the 

 same in the two groups borne by one individual ; usually tliere are five or six pits in each 

 group. They arc more strongly chitinised than the surrounding cuticle. The iippcr 

 part of their walls looks homogeneous, while the lower or apical jiortion has a cribriform 

 or sieve-like appeai-ance. HoAvever, there do not seem to be any perforations as in a true 

 sieve-plate, but merely thinner and more lightly-staining areas lying in the meshes of a 

 network of thicker substance. It has not been possible to determine whether there are 

 any glands in connection with these remarkable structures, but their appearance suggests 

 that they may be essentially the same as the pore-plates already described, though they 

 differ from them in detail. 



There is another widely-distributed kind of cutaneous gland, characterised by the 

 possession of a long, narrow, chitinous duct opening on a level with the general surface 

 of the cuticle (PL 34. fig. 15, «). The duct is a narrow tube perpendicular to the surface 



