518 HENRY M. BERNARD, 



Now , if we suppose that the original Peripatus adopted from 

 the first a hidden burrowing manner of life, a supposition borne out 

 by the very slight development of the limbs for free locomotion , it 

 would have no great use for protective bristles. And, as a matter 

 of fact, we find that Peripatus^ like many burrowing larvœ, has no 

 bristles, at least on the body. The stiff points at the tips of the 

 papillai with which the body is covered can hardly be claimed 

 as such. The disappearance of the bristles would leave their secreting 

 sacs free to develop into tracheae. 



This derivation of the tracheae in Peripatus from ordinary setiparous, 

 not from acicular, glands agrees as well with their scattered arrangement 

 as with their tendency to be arranged in rows, and further with the fact 

 that, in this latter case, the number of stigmata is considerably greater 

 than the number of the legs. We may further perhaps see in the 

 comparative insignificance of the dispersed tracheœ in Peripatus as 

 compared with the imposing branched tracheœ opening through the 

 stigmata of the Hexapoda a perpetuation of the comparative in- 

 significance of the bristle sacs by the side of those secreting the 

 acicula. 



This reference of tracheae to setiparous sacs thus explains away 

 in a very simple manner the difficulty that the tracheae of Peripatus 

 are scattered over the body, while in the Hexapoda they are regu- 

 larly and metamerically arranged. 



The slime or spinning glands on the appendages of the 2nd segment 

 have already been mentioned, and, like the sericteries of many Hexa- 

 pod larvae and the salivary glands of the imago, may be homologised 

 with setiparous glands. 



The coxal glands, which arc generally supposed to be setiparous 

 glands, will be discussed later on in connection with the Arachnida. 



Myriapoda. 



The glands of the Myriapoda are so numerous that diligent study 

 is required to unravel their homologies. In face of this difficulty, 

 we must confine ourselves here to suggesting that the deduction of 

 tracheae from setiparous sacs, either from acicular sacs or from 

 ordinary bristle sacs, will harmonise the very different arran- 

 gements of the stigmata found in this group. 



In Scutigera the tracheae are grouped into structures approaching 

 book-leaf tracheae arranged in a row down the dorsal middle line. 



