3^4 



PHYLUM ARTHROPODA 



Respiratory system. — Very long and fine unbranched tracheae are 

 widely distributed in the body ; a number open together to the exterior 

 in flask. like depressions. These openings or stigmata are irregularly 

 distributed. 



Excretory system. — A pair of nephridia lie in each segment. 

 Each consists of an internal mesodermic terminal funnel, a looped canal, 

 and a wide vesicle which opens near the base of each leg, the two last 

 parts being invaginations of the ectoderm. Nephridia are not known in 



any other Tracheate. The salivary 

 glands and the genital ducts seem to 

 be modified nephridia. It may be 

 noted that the same is probably true 

 of the " coxal glands " of Limulus 

 and of the antennary glands of 

 Crustaceans. 



Coxal or crural glands lie in the 

 legs and open to the exterior. They 

 can be in part evaginated, and they 

 probably help in respiration. In the 

 male of P. capensis the last pair are 

 very long (Fig. 203, a.g.). The large 

 mucous glands, which pour forth 

 slime from the oral papillae, are 

 regarded as modified crural glands. 



Reproductive system. — (a) 

 Female (of P. edwardsii). — From the 

 two ovaries, which are surrounded by 

 one connective tissue sheath, and 

 arise, as usual, from the coelomic 

 epithelium, the ova 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 pair of receptacula 

 seminis (for storing the spermatozoa 

 received during copulation), and a 

 pair of receptacula ovorum for storing 

 fertilised eggs. 

 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 is it 

 of mammalian gestation. The older embryos lose this " placenta," but 

 each lies constricted off from its neighbours. When born the young 

 resemble the parents except in size and colour. In P. capensis the 

 period of gestation is thirteen months. 



(6) Male (of P. edwardsii). — The male elements are produced in 

 small testes, pass thence into two seminal vesicles, and onwards by two 

 vasa deferentia into a long single ejaculatory duct, which opens in front 



Fig. 204. — Embryos of Peripatus 



capensis, showing closure of 



blastopore and curvature of 



embryo. — After Korschelt 



, and Heider. 



a., Anus ; bl., blastopore ; m., mouth ; 

 p.s., primitive segments ; w., zone 

 of proliferation. 



