PERIP'ATUS (Neo-Lat., from Ok. reptra TOS, a walking around, from reporare7s, peri)a fria, to walk around). This strange creature stand. alone, with no animals intermediate be tween itself and the worms on the one hand, and the true Arthropoda on the other. Originally supposed to be a worm, it is now referred to a class by itself, the Malaeopoda of Blainville, or Protraeheata of Ilaeckel. It lives in the tropics, in damp places under decaying wood. In general appearanee it somewhat resembles a caterpillar. but the head is soft and worm-like, though it bears a pair of antenna-like tentacles. It may be said rather to resemble superficially a leech with clawed legs, the skin and its wrinkles being like those of a leech. There is a pair of horny jaws in the mouth, but these are more like the pharyngeal teeth of worms than the jaws of arthropods. The numerous legs end each in a pair of claws. The ladder-like nervous system is unlike that of annelid worms or arthropods, but rather recalls that of certain mollusks, as well as that of certain flatworms and nemertine worms. Its annelid features are the large num ber of segmentally arranged true nephridia, and the nature of the integument. Its arthropodan features, which appear to take it out of the group of worms, are the presence of trachea., of true salivary and slime glands, of a pair of coxal glands, as well as of slaws at the end of the legs. The heart is arthropodan. being a dorsal tube lying in a pericardial sinus with many openings. This assemblage of characters is not to be found in any marine or terrestrial worm.
The trachea' are fine mbranehed tubes. without a spiral thread, and are arranged in tufts, in Prripltus Edit-a rdsii, opening by simple orifices or pores (stigmata). scattered irregularly over the surfaee of the body; but in another species ( Pcripatus ('apensis) some of the stigmata are arranged more definitely in longitudinal rows on each side, two dorsally and 11111' ventrally.
The stigmata in a longitudinal row are. however, more numerous than the pairs of legs.
The salivary glands. opening by a short com mon duet into the• under side of the month. in the same general position as in insects, are evidently, as the embryology of the a nitnal proves, trans formed nephridia, and, being of arthropodan type. explain the origin and morphology of those of insects. it is so with the slime glands, these. with the eoxal glands, being transformed and very large dermal glands. Those of insects arose in the same manner, and are evidently their homologues, while tInise of Peripatus mere prob ably originally derived from the setiparous glands in the appendages (paratpodia) of annelid worms.
The genital glands and ducts are paired, but it is to be observed that the outlets ale single and situated at the end of the body. In the male the ejaculatory duct is single; in its base a sperinato phore is found. It will be seen, then, that Peri patus is not only a composite type, and a con meeting link between worms and tracheate artho pods, but that it may reasonably be regarded, if not itself the ancestor, as resembling the probable progenitor of chilopods, myriamals, and insects, though of course there is a very wide gap be tween Peripatus and the other automate, air breathing Arthropoda.
Consult: Moseley. "On the Structure and De velopment of Peripatus Capensis." in i'kilo.sophi cal of the Mortal Society (London, (1i374 ; A. Sedgwiek, "The Development of Peri patus Capensis," parts i.. ii.. iii.. in Quarterly Journal of Microscopical Science (London, 1883 :37) ; Packard. Test-Boo' of Entomology (New York, 1898).