ONYCHOPHORA OF WEST AUSTRALIA. 375 



INTERNAL ANATOMY. 



Alimentary Canal, etc. 



The idimeutary caual presents nothiug of exceptional import- 

 ance in the way of dift'erences from tlie conditions observed in 

 otlier species of Peripatus. Tlie jaws have already been descriljed. 

 A few words are necessary with regai'd to the muscles attached 

 to them. It is frequently stated that the muscles of the man- 

 dibles a.re the only striped muscles in Peripatus. A careful 

 examination of all the muscles in the West Australian Peripa- 

 toicles has been made, but so fax- as transverse strifition is con- 

 cerned no differences can be made out between any of them. No 

 muscles bear cross-stripes, all appear smooth. 



Salivary Glands. 



Two well-developed salivary glands are pi'esent, opening by a 

 common duct ventrally into the mouth. The common median 

 duct is very short (see PI. I. fig. 1) and gives I'ise almost at once 

 to two narrow tubes which run ont at right angles to the long- 

 axis of the body and then bend suddenly backwards when the 

 lateral body-wall is reached. This portion (PI. I. fig. 1, Sal.G.d.) 

 is non-glandular, and the walls consist of compact cubical cells. 

 A marked change takes place when the ducts bend a,bruptly back- 

 wai'ds to run in the lateiul compartments in close proximity to 

 the nerve-cord ; the ducts pass here into the glandular region 

 (PL 1. fig. 1, Sal.Gl.) of the salivary gland. The cells of this 

 part are often much vacuolated, and the nuclei are pushed to the 

 bases of tlie cells, where they lie in close proximity to a thin 

 muscle and connective-tissue sheath (see PI. II. fig. 5). 



The length of the salivary glands is such that they extend back 

 to somewheie about the 7th or 8th pair of legs — that is to say, 

 just beyond the middle of the body. 



The Trache.e. 



The respiratory organs of Peripatus ha.ve always been regarded 

 as of special note in view of the interesting relationships of the 

 Onyciiophora. It is somewhat surprising, then, to find that even 

 to-day there is some doubt as to whether a spiral fibre is present 

 in the tracheal vessels. Other points are also uncertain. 



The respira.tory organs, as is well known, consist of trachea?. 

 These are very delicate and of minute diameter. In the West 

 Australian Peripatoides they could only be made out with diffi- 

 cnlty in preserved specimens, although more easily in sections. 

 They are, however, exceedingly clear when fi'eshly killed speci- 

 mens are dissected under water and examined with a Zeiss 

 binocular dissecting microscope. Ample material has rendered 

 tliis mode of examination possilde. 



Dlstrihuiion of Trachece. — As is well known, the trachea^ of 



