DE VEL 0PM ENT OF PERIPA TUS. 253 



organs are represented by two simple eyes on the top of the head. 

 'J'hese are most like the eyes of some marine Annelids. Behind each 

 there lies a special optic lobe connected with the brain, but the eye 

 itself arises as a dimple in the skin. 



Alimentary Canat. — Round about the mouth, papillfe seem to have 

 fused to form a " mouth-cavity," which includes the mandibles, a median 

 pad or tongue, and the opening of the mouth proper. The mouth leads 

 into a muscular pharynx, into which opens the common duct of two 

 large salivary glands, which extend far back along the body. Mouth, 

 pharynx, and short oesophagus are lined by a chitinous cuticle, like that 

 of the exterior. The long digestive region or mid-gut extends from 

 the second leg nearly to the end of the body. Its walls are plaited. 

 Finally, there is a short rectum, lined by a chitinous cuticle. 



Circulatory System. — The dorsal blood-vessel forms a long contractile 

 heart. It lies within a pericardial space, and receives blood by seg- 

 mentally arranged apertures with valves. The circulation is mostly in 

 ill-defined spaces in the body-cavity, which has therefore been called a 

 " heemocoele." 



The Respiratory System consists of very long and very fine unbranched 

 tracheje, which are widely distributed in the body ; a number open 

 together to the exterior in flask-like depressions. These openings or 

 stigmata are diffuse and irregular in Feripatus edwardsii, but in P. 

 capensis there is a dorsal and ventral row on each side. In P. nova- 

 zealandia the tracheae are said to be branched. 



The Excretory System. — A pair of nephridia lie in each segment. 

 Each consists of an internal terminal funnel, a looped canal, and a wide 

 vesicle which opens near the base of each leg. They are not very differ- 

 ent from those of many Annelids, but their occurrence in a Tracheate 

 is remarkable. The salivary glands, the genital ducts, and two anal 

 glands opening near the anus are regarded as modified nephridia. It 

 may be noted, too, that the same is perhaps true of the " coxal glands " 

 of Limulus and of the antennary glands of Crustaceans. 



Crural or Coxal Glands lie in the legs and open to the exterior. 

 Their meaning is uncertain, their occurrence is variable. Thus in P. 

 edwardsii they occur in the males only, in P. capensis they are present in 

 both sexes. The large mucus glands, which pour forth slime from the 

 oral papillsB, are regarded as modified coxal glands. 



Reproductive System. — (a) p'emale (of P. edwardsii). — From the twO' 

 ovaries, which are surrounded by one connective tissue sheath, the eggs 

 pass by two long ducts leading to a common terminal vagina opening' 

 between the second last legs. These ducts are for the most part uteri, 

 but on what may be called the oviduct portions adjoining the ovaries, 

 there are two pairs of pouches — (a) a pair of receptacula seminis (for 

 storing the spermatozoa received during copulation), and a pair of 

 receptacula ovorum for storing fertilised eggs. In P. capensis the ovary 

 is halved rather than paired, and there are a few; other differences 

 between the species. In male and female alike, of this species at least, 

 the ducts are not in direct connection with the reproductive organs. 



The eggs are hatched in the uteri, and all stages are there to be 

 found in regular order. The young embryos seem to be connected to 

 the wall of the uterus by what has been called a ' ' placenta, "' so suggestive 



