360 J. E. BLOMFIELD. 



the secretion, supported by a stroma, and it is possible to 

 trace the continuity of the cells in the gland with those of 

 the epidermis through the stalk of the invagination, so that 

 the fibrous wall is obviously continuous with the dermis, and 

 the cell elements of the gland with those of the epidermis. 



If the contents of a gland be squeezed out and received 

 on a slide {cf. fig. 5) and examined, they are seen to be 

 composed of a quantity of large oblong yellow cells, which 

 appear to be unwinding, and giving origin to long coiled 

 and twisted threads running in various directions across the 

 field of the microscope. Besides these are others bearing a 

 considerable resemblance to spiders, which appear to form a 

 stroma for the support of the other cells. These *' spider 

 cells '' are found in specimens preserved in spirit. 



Of these two structures, the first, which we will designate 

 ''thread cells" {cf. fig. 6), are of particular interest, from the 

 peculiarity of their construction. In shape they do not 

 exhibit much variation. They are always oblong, some- 

 times larger at one end than the other, but generally more 

 or less ovoid. They stain very readily with picric acid of a 

 bright yellow hue, and under the action of carmine exhibit 

 a nucleus or remains of such at one of the poles (the head). 

 This, which in the unstained cell seems to be of the nature 

 of a vacuole, after long treatment with staining fluids, is 

 seen to be a nucleus, often containing one well marked and 

 comparatively large nucleolus. On careful focussing when 

 examining the mature cells it is seen that the yellow mate- 

 rial is divided into threads, which are wound round a central 

 core of granular matter. The exact mode in which the 

 thread is wound is rather hard to determine, but it seems 

 that most superficially it is arranged transversely to the long 

 axis of the cell, while in the next layer it runs parallel with 

 it (fig. 7). When the cell is mature and while it is in the 

 gland, or after its discharge, it begins to unwind. This 

 process begins at the pole opposite the nucleus, and it seems 

 that the cell is unravelled by a single thread. These 

 threads are found in the mucus at the surface of the body 

 of the animal in association with epidermic and goblet cells. 



In sections of a young gland [cf. fig. 8) where the ele- 

 ments are not mature, it is possible to trace the origin of 

 the thread cells from the ordinary epidermic cells. As has 

 been stated above, the glands are to be regarded as solid 

 involutions of the epidermis, in which the various epidermic 

 cells undergo a change in connection with the secretion of 

 mucus, and these two elements — the " thread cells " and 

 " spider cells " — may be seen to have their origin from ordi- 



