COMPARATIVE MOEPBOLOGY OF THE GALEODID.E. 331 



suddenly thickened, without, however, breaking their continuity {cf. PI. XXXI. fig. 7). 

 A similar sudden thickening of the chitinogenous strata forms the crenulations of the 

 tracheal tubes (PI. XXX. tig. 111). 



Myjjodermis. — The cells secreting these layers of chitin are not always demonstrable ; 

 in some places, especially w here the innermost layers take stain, they appear to be embedded 

 in the cliitin which they are secreting. At other places, especially where the cuticle is 

 very thick, the hypodermis-cells are very regular and distinct, Avith large staining nuclei. 

 They are sometimes cylindrical and rest on a basal membrane running parallel with 

 the cuticle (PI. XXX. fig. 4) ; at others they are plate-like, and so closely applied to the 

 chitin that they are seen only in well-stained preparations. In this latter case staining 

 processes from the cells run at riglit angles through the chitin, and in cases where (in 

 sections) the hypodermis has parted from the chitinous layers, these processes break ofi, 

 are left in the chitinous layers, and are seen in small groups of deeply stauiing points 

 (PL XXIX. fig. 15). The concentrated grouping and staining of these points suggest that 

 the processes tliemselves came from the nuclei. The fact that in those cases where the 

 cells are not demonstrable they are probably altogether, both cytoplasm and the nucleus, 

 embedded in the chitin, shows that there is nothing improbable in. the nuclei sending 

 processes into the cuticle in the cases in question. 



Migration of Pigment-cells into the Cuticle. — The incorporation of other matter into the 

 cuticle is clearly seen in Galeodes. In almost all parts, streams of black dots may be seen 

 running up the traversing canals (PL XXIX. tig. 17). These may be pigment-granules. 

 No doubt, indeed, exists as to the wandering of pigment-cells into the cuticle at certain 

 definite places, e. (j. in the pedipalps. An enormous number of dark green pigment masses 

 are formed in the distal portions of these limbs, and they find thek way to the chitin either 

 of the outer cuticle or of the tendons and the tracheae. Among the tissues they are either 

 small round bodies, or grouped to form long, straggling, tangled syncytia. On reaching 

 the cuticle, they become fusiform and applied lengthwise to the chitin, through which 

 they ascend by sending processes into it. These processes tend to spread out between the 

 principal layers of the chitin (PL XXIX. fig. 16; cf. also PL XXVIII. fig. G). In this 

 way, the whole of the fusiform body may come to lie within the cuticle, between its separate 

 layers. I know nothing more of its fate, either here or on the tendons or ti-achete. The 

 gravitation of these cells towards the chitin is of itself interesting. It is not easy to 

 avoid suggesting that the cells are collecting and removing waste matter from the ends 

 of these long limbs, where they are most plentiful and where the circulation is probably 

 sluggish. 



Takiug the cuticle of an adult Lycosa for compansoa, the chief point noticed was that it was 

 much more brittle than that of Galeodes. Microscopic examination shows that a greater number of 

 the chitin layers are hard and refractive tlian in Galeodes. I have counted ten distinct hard red-brown 

 layers, whereas the softer white chitin layers so numerous in Galeodes arc comparatively few. It is thus 

 very difficult to get sections of this Spider. It is possible that this increase in the hardness of the 

 whole cuticle permits of its being thin and therefore lighter in adaptation to the semi-aerial life on webs 

 characteristic of the Spiders (though this would not apply to Lycosa). 



The cuticle of Scorpio {Euscorpio) is characterized by the specialization of a very clear glassy layer of 



44* 



