OF PERIPATUS CAPENSIS. 895 



which give such an Arthropod appearance to these organs in 

 Peripatus. 



The arrangement of the cells in the bodies just described led 

 me at first to look upon them as glands, but a further inves- 

 tigation induced me to regard them as a form of tactile organ. 

 The arguments for this view are both of a positive and a nega- 

 tive kind. 



The positive arguments are the following : 



(1) The organs are supplied with large nerves, which is dis- 

 tinctly in favour of their being sense organs rather than glands. 



(2) The peculiar striae at the base of the spines appear to me 

 like the imperfectly preserved remains of sense hairs. 



(3) The distribution of these organs favours the view that 

 they are tactile organs. They are most numerous on the an- 

 tennas, where such organs would naturally be present, especially 

 in a case like that of Pe'ripatus, where the nerve passing to 

 the antennas 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 im- 

 portant 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 unfavourable to the view that they are 

 glands, as it is favourable 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 



