1915] The Ottawa Naturalist. 137 



widely separated ventral nerve cords, without serial ganglia, 

 and especially in the paired sympathetic nerves on the pharynx 

 and oesophagus, the pharynx being markedly muscular. The 

 simple eyes (one pair), the numerous paired segmental organs 

 or nephridia, of which the outer and the internal vesicle are 

 really coelomic, while the first pair become the large salivary 

 glands, as in some Oligochaetes ; the short stomodaeum and 

 proctodaeum (or anterior and posterior sections of the alimentary 

 canal), the hollow, sac-like limbs, and the soft, delicate integu- 

 inent, without a dense, hard exoskeleton and the presence of 

 cilia are all worm features.* But Peripaius is also a Tracheate, 

 for like insects it breathes by tracheal tubes opening by external 

 stigmata, its limbs show slight segmentation and some are 

 modified as mouth-organs, it has antenna^, and the heart and the 

 generative organs are coelomic, the ova and sperms being 

 derived from the walls of the coelom. All these features are in 

 contrast to the Annulates and connect Peripaius with the Tra- 

 cheates, and therefore the Insects. "I believe it to be," said 

 Moseley, "a nearly related representative of the ancestor of all 

 air-breathing Arthropoda i.e., of all insects, spiders and myria- 

 pods. It is impossible here to consider the profoimdly inter- 

 esting nature of the body-chamber, which is a haemocoel, and 

 not a coelom or true body-cavity at all, certain portions of the 

 true coelom alone persisting as in the segmental or nephridial 

 spaces, and the generative glands. The study of Peripaius 

 throws a flood of light tipon the origin of many of the most 

 important features in the Tracheates, it is indeed the Proto- 

 tracheate and forms an entire class to itself, a class with one 

 genus only. But on the other hand it is an Annulate and has 

 features in common with Molluscs and Echnoderms. There is 

 probably no more generalized type of animal living and it may 

 be justifiably maintained that it is therefore the most interesting 

 and possibly the most ancient of metazoan stem-forms. If Peripa- 

 ius preceded the Annulates and Tracheates and was the ancestor of 

 all the worms, insects, spiders and myriapods, why have we 

 not some fossil remains in some of the early fossiliferous strata? 

 Peripaius is such a frail, soft creature that excepting for the hard 

 jaws with four sickle-shaped cutting blades; the chitinous 

 jaw-levers or so-called buccal tracheal pits, first correctly de- 

 scribed and interpreted by Dr. C. Gordon Hewitt; the minute 

 occelli or simple eyes, the chitinous claws, minute external spines 

 and the tracheal tubes, no remains could be readily preserved 



*The two muscular layers, circular and longitudinal and unstriped, are 

 worm features; the fibres of the jaw-muscles are, however, striped (see 

 Dr. C. Gordon Hewitt "Buccal Pits of Peripatus" Proc. Manchester Lit. 

 and Philos. Soc, Vol. SO, Oct. 21, 1905). 



