vi PROTRACHEATA 437 



is a ladder nervous system, which shows striking similarity with that of the Amphi- 

 neura, Placophora, and Zeugobranchia among the Mollusca, and that of certain Platodes 

 and Nemertina. There is no doubt, however, that the ladder nervous system of 

 Peripatus is homologous with the brain and ventral cord of the Annulata and 

 Arthropoda. Its specifically deviating form may be regarded in two ways : (1) The 

 ladder nervous system of Peripatus has arisen out of a typical ventral cord by the 

 moving apart of its symmetrical halves and the increase of the transverse commissures ; 

 (2) in contrast with the ventral cord of the Annulata it represents a more primitive 

 condition. The latter view seems to us the more plausible, since we adhere to the 

 opinion that the ventral cord of the Annulata itself proceeded from a ladder-like 

 nervous system by the moving together of the longitudinal trunks towards the ventral 

 middle line. Peripatus, according to this view, would be related only to the typically 

 segmented racial form of the Annulata. The fact is perhaps not without significance 

 that the Phyllopoda also (w T hich are held to stand nearest of all the living Crustacea 

 to the racial form) possess a ladder-like nervous system. The large number of trans- 

 verse commissures in each segment must be a secondary condition. In a few 

 Annulata we find more than one transverse commissure, also probably as a secondary 

 condition ; the same is also the case in the Phyllopoda. 



The tracheae of Peripatus may perhaps be regarded as dermal glands transformed 

 by adaptation to life on land, glands similar to those long mostly unicellular dermal 

 glands which in certain Hirudinea and many Turbellaria spread far through the 

 body parenchyma. 



From the point of view of Comparative Anatomy it is of the greatest importance 

 to have proved that the salivary glands and genital ducts are transformed nephridia, 

 helping us as it does to understand the morphological significance of these organs in 

 the Trachcata. No less important is the almost certain proof that the slime and 

 coxal glands are homologous, and that these dermal glands are homologous with 

 the setiparous glands of the Annulata, especially with reference to similar glands 

 in the Traclieata. 



It cannot be certainly proved that the antennse, jaws, and oral papillae of Peripatus 

 .correspond with the antennse mandibles, and one pair of maxillae of the Tracheata. 



Single genus : Peripatus. Animals avoiding light, and living on land in damp 

 places, under the bark of old trees, under stones, etc. P. capensis : on the wooded 

 slopes of Table Mountain, Cape of Good Hope. P. Edivardsii : Venezuela ; related 

 species in Trinidad. P. Novce Zealandice ; P. Leuckartii : Australia. 



Literature. 



H. N. Moseley. On the Structure and Development of Peripatus capensis, in Philos. 



Transactions. Vol. CLXIV. 1874, and in Proc. Roy. Soc. No. 153. Vol. 



XXII. 1874. 

 F. M. Balfour. The Anatomy and Development of Peripatus capensis. Quart. Journ. 



Microsc. Science. Vol. XXIII. 1883. 

 J. v. Kennel. Entwicklungsgeschicte von Peripatus Edivardsii und P. torquatus. I. u. 



II. in Arbeiten Zool. Inst., Wiirzburg. Vols. VII. and VIII. 1885 to 1886. 

 E. Gaffron. Beitrdge zur Anatomie und Histologie von Peripatus, in Schneider's 



Zool. Beitrdge. Vol. I. 1883. 1885. 

 A. Sedgwick. A Monograph of the Development of Peripatus capensis, in Studies 



from the Morphological Laboratory in the University of Cambridge. Vol. IV. 



London, 1888. Also in Quart. Journ. of Micros. Science. 



In these Treatises also further Bibliography. 



