436 



COMPARATIVE ANATOMY 



CHAP. 



duct also, however long and coiled it may be. The salivary glands in the young 

 recently hatched animal still function as nephridia and have funnels opening towards 



the body cavity, which afterwards close but are 

 still retained in the adult animal as vesicular 

 appendages. Their nephridial ducts grow out far 

 beyond the funnels to form blindly ending tubes 

 posteriorly. Their apertures approach the middle 

 line by the growing up of the oral enclosure and 

 thus reach the floor of the buccal cavity. A new 

 median invagination of the integument then yields 

 their impaired duct. The genital ducts represent 

 the nephridia of the penultimate limb -bearing 

 segment and develop in a similar manner (Fig. 300). 

 At first their outer apertures lie laterally, and 

 apart. Later they approach the middle line. The 

 uteri in the female and vasa deferentia in the male, 

 which correspond with the nephridial canal of the 

 typical nephridia, are joined by a new median 

 unpaired invagination from without, and from this 

 proceed, in the male the ductus ejaculatorius, and 

 in the female the vagina. 



The brain and longitudinal nerve trunks arise 

 as paired thickenings of the ectoderm, which differ- 

 entiate from before backward and separate from 

 the ectoderm. The rudimentary ganglia of the jaw 

 segment fuse at a later stage with the rudimentary 

 ganglia of the head segment to form the brain. 



FIG. 300. A, B, C, Diagrammatic 

 representation of the development 

 of the female sexual apparatus of 

 Peripatus Edwardsii in transverse 

 sections (after v. Kennel), ov, Ovary, 

 proceeding from the median portion 

 of the mesoderm sac ; ml, that part of 

 the female genital apparatus which 

 corresponds with the nephridial fun- 

 nel, and from which proceed chiefly 

 the receptaculum ovorum and the 

 piece which connects the uteri with 

 the ovaries ; ee, paired ectodermal in- 

 vaginations, which become the uterus. 

 In B the two invaginations have ap- 

 proached each other in the middle 

 line, and in C at this point a new 

 unpaired ectodermal invagination (va) 

 has appeared, the rudiment of the 

 vagina ; d, intestine ; n, longitudinal 

 trunks of the nervous system. 



The Systematic Position of Peripatus. 



If we try to estimate what has been said about 

 the organisation and development of this animal 

 from a comparative point of view, we come to the 

 conclusion that Peripatus unites typical Annulatan 

 characteristics with typical Arthropodan and espe- 

 cially Tracheatan characteristics. The following 

 are its Annulatan characteristics : (1) segment- 

 ally arranged nephridia of the type of the per- 

 manent trunk nephridia of Worms ; (2) segment - 

 ally arranged coxal glands, which are undoubtedly 

 homologous with the Chsetopodan setiparous 

 glands ; (3) a dermo-muscular tube, which most 



nearly approaches that of the Hirudinea. The 



truncated form of the extremities and the structure of the eye are less significant. 

 The following are the Arthropodan and especially Tracheatan characteristics of Peri- 

 patus: (1) the respiratory organs developed in the form of tracheae ; (2) the dorsal 

 heart lying in a pericardial sinus and supplied with many pairs of ostia, and 

 the lacunar circulatory system ; (3) the transformation of extremities into mouth 

 parts (jaws) ; (4) the specific form of the salivary glands. 



The nervous system deviates in a characteristic way from the somewhat similar 

 nervous system of the Annulata and of the Arthropoda, by the lateral position of the 

 ventral longitudinal trunks, the slight development of the ganglia, and the large 

 number of transverse commissures in each segment. The nervous system of Peripatus 



