I SPECIES 23 



of the body. In the anterior somites it dwindles and disappears, 

 but in the posterior part it unites with the dorsal divisions of 

 contiguous somites of the same side, and forms a tube the 

 generative tube (Fig. 14, D, 2). The last section of this tube 

 retains its connexion with the ventral portion of the somite, and 

 so acquires an external opening, which is at first lateral, but soon 

 shifts to the middle line, and fuses with its fellow, to form the 

 single generative opening. The praeoral somite develops the 

 rudiment of a nephridium, but eventually entirely disappears. 

 The jaw somite also disappears ; the oral papilla somite forms 

 ventrally the salivary glands, which are thus serially homologous 

 with nephridia. The perivisceral cavity of Feripatus is, as in all 

 Arthropoda, a haemocoele. Its various divisions develop as 

 a series of spaces between the ectoderm and endoderm, and 

 later in the mesoderm. The mesoderm seems to be formed 

 entirely from the proliferation of the cells of the mesoblastic 

 somites. It thus appears that in Feripatus the coelom does not 

 develop a perivisceral portion, but gives rise only to the renal 

 and reproductive organs. 



APPENDIX^ 



Peripatus, Guilding 



Soft-bodied vermiform animals, with one pair of ringed antennae, one 

 pair of jaws, one pair of oral papillae, and a varying number of claw-bearing 

 ambulatory legs. Dorsal surface arched and more darkly pigmented than 

 the flat ventral surface. Skin transversely ridged and beset by wart-like 

 spiniferous papillae. Mouth anterior, ventral; anus posterior, terminal. 

 Generative opening single, median, ventral, and posterior. One pair of 

 simple eyes. Brain large, with two ventral hollow appendages ; ventral 

 cords widely divaricated, without distinct ganglia. Alimentary canal simple, 

 uncoiled. Segmentally arranged, paired nephridia are present. Body cavity 

 is continuous with the vascular system, and does not communicate with the 

 paired nephridia. Heart tubular, with paired ostia. Eespiration by means 

 of tracheae. Dioecious ; males smaller and generally less numerous than 

 fe.males. Generative glands tubular, continuous with the ducts. Viviparous. 

 Young born fully developed. They shun the light and live in damp places 

 beneath stones, leaves, and bark of rotten stumps. " They eject when irritated 

 a viscid fluid through openings at the apex of the oral papillae. Distribu- 



^ Gf., in addition to the works quoted on pp. 3, 4 : A. Willey, " Peripatus novae- 

 hritanniae,'' in. Zoological Results, i. , Cambridge, 1898 ; L. Bouvier, "Cont. a I'histoire 

 des Peripates americains," Ann. Soc. Entomol. de France, Ixviii., 1899; "W. F. 

 Purcell, "Anatomy of Opistliopatus cinciipcs," Annals of the S. African Museum, 

 ii. 1900. R. Evans, Quart. J. Micr. Sci. xliv., 1901, pp. 473, 539. 



