432 COMPARATIVE ANATOMY CHAP. 



but appear temporarily in the course of development. It has also 

 been ontogenetically proved that the salivary glands are the trans- 

 formed nephridia of the segment carrying the oral papillae 

 which has fused with the head ; this is of extreme importance. 

 Two blindly ending canals which open into the oral cavity near the 

 base of the jaws have been pointed out as nephridia of the jaw 

 segment reduced to their eetodermal portion. 



Respiratory Organs. It is a fact of great importance that Peripatus 

 possesses the respiratory organs which are characteristic of the Tracheata, 

 and which occur only in them. They consist of long, very fine, and 

 thin chitinous tubes filled with air and widely dispersed through the 

 body ; in Peripatus they are not branched ; they emerge united into 

 tufts at the base of a flask -shaped depression of the integument. 

 The outer aperture of such a depression may be called, as in the 

 Tracheata, the stigma. In P. Edwardsii the stigmata occur in great 

 numbers and quite irregularly all over the surface of the body. In 

 P. capensis, on the contrary, at least some of the stigmata show a definite 

 arrangement, viz. in longitudinal rows on each side two, one dorsally 

 and one ventrally. The stigmata in a longitudinal row are, however, 

 more numerous than the pairs of legs. 



Leg Glands (eoxal glands) and Slime Glands. In Peripatus 

 capensis, in both sexes, there are paired glands emerging on the under 

 side of the extremities, and only wanting in the first pair of trunk 

 limbs. Every such coxal gland consists of a sac lying in the lateral 

 division of the body cavity, and of a duct. The coxal glands of the 

 last pair of feet are extraordinarily long in the male, and stretch far 

 forward to near the middle of the body (Fig. 293, cd). In P. Edwardsii 

 leg glands occur only in the males, not in each segment, but only in a 

 certain number of segments lying in front of the genital segments ; 

 one, two, or three glands may occur in each limb. 



There are two largely -developed thickly -branched slime glands 

 (Fig. 293, sd), which must be considered as transformed leg glands, 

 reaching far back into the body cavity. Their ducts run forward to 

 emerge at the ends of the oral papillae. When the animals are 

 irritated, these glands forcibly eject a secretion consisting of a tangle 

 of viscid threads. 



Sexual Organs. The sexes are separate. The best known sexual 

 organs are those of P. Edwardsii. Those of other species seem in many 

 points to be differently formed. (1) Female sexual apparatus (Fig. 

 295). This is as a rule paired. The two lateral halves, however, are 

 connected at two points ; first, where the ovaries pass into the uteri, 

 and second, to form the unpaired terminal division (vagina) leading to 

 the exterior. The two ovaries are imbedded in a common envelope 

 of connective tissue, and suspended to the pericardial septum in the 

 median line by a ligament consisting of two muscles. They lie in the 

 posterior portion of the body cavity. They are continued into the two 

 uteri, which, close to the ovary, are united by an unpaired portion ; 



