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



tations of a secreting apparatus, it is in the first place provided 

 that the blood vessels approach some free surface from which the 

 secretion is poured out. The vessels, however, do not open upon the 

 secreting surface, for the coats as well as the tissues covering them 

 are permeable to liquids ; and the most favourable conditions for 

 the discharge of fluid are ensured by the division of the vessels 

 into their finest or capillary branches, and by the arrangement of 

 these capillaries in close order as near as possible to the surface. 

 In this way their coats are reduced to the greatest degree of 

 tenuity and simplicity, and the blood brought into contact with the 

 permeable parietes of its containing channels, as well as effectually 

 and by reason of its slow motion, for a long time exposed to those 

 influences, whether operating from within or without the vessels, 

 which promote transudation." 



One of the elements of this process is the extension of the 

 surface over which the blood may be exposed ; it may either be 

 spread otit like the sweat glands in the skin, or it may be drawn 

 into complicated folds, as in the kidney ; but, however accomplished, 

 the blood must be brought into contact with the layer of secreting 

 cells by which the peculiar elements are withdrawn. We have 

 various examples of the types upon which the glands were formed 

 depicted in the diagram taken from Quain and Sharpey's Anatomy, 

 and by it you will see that whatever the form of the gland, the 

 elements entering into it are a layer of capillary blood vessels, a 

 basement membrane, and a layer of secreting cells. The glands 

 may be simple membranes with a plain secreting surface, or they 

 may be pouch-like inflections of that surface, or these pouches may 

 have pouches again on their walls, and so the gland may become 

 sacculated or lobular. Those of you who have read Mr. Lowne's 

 valuable monograph on the anatomy of the Blowfly, will remember 

 his drawing of the salivary glands of that insect, and will readily 

 recognise in it the simple tubular character of the gland, while a 

 reference to the salivary glands of the Cockroach which I exhibit 

 under my microscope, will give you a very good illustration of 

 glands of the compound or lobulated kind. These organs occupy 

 in the Cockroach the same position as the salivary glands of the 

 fly, and are analogous to them in function without a doubt; 

 they are situated in the anterior part of the thorax, and 

 in front of the anterior thoracic ganglion from which they 

 may derive part of their nerve supply; to expose them, it 



