ANATOMY AND DEVELOPMENT OP PELIIPATUS OAPRNSIS. 239 



the antennae is simply gigantic. On the other hand, the an- 

 tennae would not be a natural place to look for an enormous 

 development of dermal glands. 



The lips^ oral papillae, and under surface of the legs, where 

 these bodies are also very numerous, are situations where tactile 

 organs would be of great use. 



Under the head of negative arguments must be classed those 

 which tell against these organs being glandular. The most 

 important of these is the fact that they have no obvious 

 orifice. Their cavities open no doubt into the spines, but 

 the spines terminate in such extremely fine points that the 

 existence of an orifice at their apex is hardly credible. 



Another argument, from the distribution of these organs 

 over the body is practically the converse of that already used. 

 The distribution being as unfavorable to the view that they 

 are glands, as it is favorable to that of their being sense 

 organs. 



The Tracheal System. 



The apertures of the tracheal system are placed in the de- 

 pressions between the papillae or ridges of the skin. Each of 

 them leads into a tube, which I shall call the tracheal pit (fig. 

 30), the walls of which are formed of epithelial cells bounded 

 towards the lumen of the pit by a very delicate cuticular 

 membrane continuous Avith the cuticle covering the surface of 

 the body. The pits vary somewhat in depth ; the pit figured 

 was about 0*09 mm. It perforates the dermis and terminates 

 in the subjacent muscular layer. The investigation of the 

 inner end of the pit gave me some little trouble. 



Transverse sections (fig. 30) through the trunk containing a 

 tracheal opening show that the walls of the pit expanded 

 internally in a mushroom-like fashion, the narrow part being, 

 however, often excentric in relation to the centre of the expanded 

 part. 



Although it was clear that the tracheae started from the 

 expanded region of the walls of the pit, I could not find that 

 the lumen of the pit dilated into a large vesicle in this part. 



