Cytological studies on tlie spinning glands of Platypliylax etc. 405 



in this respect. He found the microsomes were always present and uni- 

 formly stained darker than the macrosomes. Meves [16] says, „Die Kerne 

 der Spinndrüsen der Raupen sind ausserordentlich reich an Chromatin. 

 Dieses ist in Form kleiner, fast durchweg gleichgrosser Körner (der Micro- 

 somen Korscheits) vorhanden; ausnahmsweise kommen auch grössere 'An- 

 sammlungen von Chromatin in Form von Klumpen vor." He also found 

 that in some preparations many of these large irregular masses, nucléoles, 

 enclose one or many small vacuoles. The chromatin granules were 

 observed by Meves [16] to often lie in strings of lightly colored sub- 

 stance, linin; this he did not, however, find true in sublimate preparations. 



What these two observers have seen in the spinning glands of 

 the Lepidoptera we found, with but slight variations, in Platyphylax. 

 We have already spoken of the nucleus as seen in surface view and 

 will now confine ourselves to a study of sections. In speaking here- 

 after of a surface view we refer to the first sections cut in making 

 a longitudinal series; in many of these a fairly large portion of a 

 nucleus may be present. From the shape of the nuclei it is at once 

 obvious, tha.t, in different parts of the sections, it will vary much in 

 size and form; also, that the same general view of it will be obtained 

 in either a transverse or a longitudinal section of the gland. Most of 

 the glands were cut longitudinally, thus making the sections fewer and 

 much larger than if cut transversely. 



Normal glands (B^igs. 9 and 10). The cytoplasm in the normal 

 glands fails to show any differentiation in the various parts of the 

 cell; it appears dense, granular, stains evenly and deeply and, from 

 its structure, appears the same in all parts of the cell. It, in almost 

 all specimens, presents an appearance free from vacuoles and is quite 

 compact. Normal glands were, however, examined, which showed the 

 cytoplasm different from this in that a marked contrast between that 

 of the outer and that of the inner half of the cells was noticeable. 

 The former part shows in these few rather exceptional cases a fairly 

 distinct striation, at right angles to the surface of the gland, such as 

 is much more pronounced in glands which have been active. 



A tunica propria is distinctly seen on the outer surface of the 

 gland and jnst within this the outer membrane, which is best seen 



