T. C. WHITE ON THE SALIVARY GLANDS OF THE COCKROACH. 6 



is necessary to remove the segment carrying the first pair of legs, 

 when upon searching amongst the muscular debris left by that 

 removal, the glands will readily be found attached to the oesophagus 

 on either side. They are of a twofold character, being made 

 up of two sacs and two compound glands. The salivary sacs 

 are not at first readily distinguishable as sacs, as they are collapsed 

 and not inflated as the air sacs of insects usually are — they 

 appear to be formed of two coats, the external being composed of 

 nucleated membrane, while the internal coat appears to be base- 

 ment membrane carrying a layer of columnar epithelium. The 

 sacs communicate with the mouth by means of ducts which unite 

 as a common channel as they emerge from the anterior part of the 

 thorax. The ducts bear a general resemblance to the tracheal 

 tubes, but of a larger calibre, a slight constriction being noticeable 

 at the point of their union with the sacs, but nothing resembling 

 the valve pointed out by Mr. Lowne as existing in the salivary 

 duct of the fly exists in the case of the Cockroach. More closely 

 attached to the outside of the oesophagus, and lying between it and 

 the salivary sacs, the glands may be found spread out as a layer : they 

 are exceedingly delicate, and require very tender manipulation to 

 detach them from the oesophagus, which they embrace very closely. 

 Upon a more minute examination, they will be seen made up into a 

 number of lobes, like a bunch of grapes, each lobe being a congeries 

 of cells, attached by fibres of connective tissue to adjoining lobes. 

 Between the cells small passages may be observed which form 

 the beginnings of fine tubes, these, coalescing with others, ulti- 

 mately join to form the principal duct, which running on by the 

 side of the duct of the salivary sac meets its fellow of the opposite 

 side a short distance anterior to the bifurcation of the two ducts 

 of the salivary sacs, the four ducts there uniting and entering into 

 the formation of a common duct, which eventually opens on the 

 upper surface of the labium. The supply of nerves to these glands 

 has been a point of great difficulty, and I have not made a 

 demonstration of them that I can positively rely on, but I believe 

 that the common duct passes down between the ganglionic cords, 

 and there receives some of the fibres of the anterior ganglion, but 

 you can easily imagine that in a dissection of this kind, where great 

 delicacy of touch and manipulation is required, that many of these 

 fine nervous fibres would of necessity be ruptured and their traces 

 lost. 



