5(32 ZOOLOGY SECT. 



each pair of legs. It is enclosed in a pericardial sinus imperfectly 

 cut off from the general body cavity by a longitudinal partition. 

 There are no other vessels with the exception of a median ventral 

 vessel. 



The organs of respiration are delicate, unbranched or rarely 

 branched, tracheal tubes lined with a thin chitinous layer exhibiting 

 fine transverse striations. Groups of these open in little depres- 

 sions of the integument, the external openings of which are 

 known as the stigmata. The stigmata in some of the species are 

 distributed irregularly over the surface ; in others are arranged 

 in longitudinal rows. By means of these tubes air is conveyed to 

 all parts of the body. 



A series of pairs of glands, the coxal glands (Fig. 444. 

 cox. gld.), lie in the lateral compartments of the body cavity, and 

 their ducts open on the lower surfaces of the legs. Their distri- 

 bution varies in the two sexes and in the different species : in 

 one species P. edwardsii they are only developed in the male. 

 A pair of larger glands the slime glands (si. gld.) opening at 

 the extremities of the oral papilla?, may be modified coxal glands : 

 the secretion of these is discharged in the form of a number of 

 fine viscid threads when the animal is irritated, and appears to 

 serve a defensive purpose. 



The nervous system consists of a brain (brn.) situated in the 

 head, and of two longitudinal nerve cords (ne. co.) which run parallel 

 with one another throughout the body to the posterior end, where 

 they join together behind the anal aperture. A number of very 

 fine transverse commissures, more numerous than the segments, 

 (i.e. than the pairs of limbs) connect the two cords together to 

 form a ladder-like nervous system comparable to that of some of 

 the Flat Worms. The cords are very slightly swollen opposite 

 each pair of limbs : nerve cells cover them uniformly throughout 

 their entire length. The brain gives off nerves to the antenna 1 '. 

 The nerves to the jaws are given off just where the brain passes 

 into the longitudinal nerve cords. 



The excretory organs are'nephridia (Fig. 445) of the type of 

 those of the Annulata, situated in pairs in the lateral compartments 

 of the body cavity, and opening on the lower surfaces of the legs at 

 their bases. Each nephridium consists of a wide funnel (tr.) with 

 fringed margins opening into the ccelome or into a closed sac ; a 

 looped tube (sg.) ; and a dilated terminal vesicle (eb.), situated close 

 to the external opening. The salivary glands and the reproductive 

 ducts are, as shown by the study of their development, specially 

 modified nephridia, as appear also to be a pair of glands the ana 

 glands opening close to the anus. 



Reproductive organs. Peripatus has the sexes distinct. I 

 the female there are two ovaries and two uteri, the latter in the 

 form of long curved tubes which unite behind in a median vagina 



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