DEVELOPMENT OF PEKIPATUS CAPENSIS. 
777 
Speculations as to the mode of origin of the trachese themselves in the Tracheata 
are many. Prof. Haeckel * follows Gegenbaur, whose opinion is expressed in his 
£ Grundziige der vergleichenden Anatomie,’ 2nd edit. p. 441. Gegenbaur concludes 
that tracheae were developed from originally closed tracheal systems through the inter- 
vention of the tracheal gills of primaeval aquatic insects now represented as larvae. If 
Peripatus be as ancient in origin as is here supposed, the condition of the tracheal 
system in it throws a very different light on the matter. Peripatus is the only Tracheate 
with tracheal stems opening diffusely all over the body. The Protracheata probably 
had their tracheae thus diffused, and the separate small systems afterwards became con- 
centrated along especial lines and formed into wide main branching trunks. In some 
forms the spiracular openings concentrated towards a more ventral line (lulus) ; in others 
they took a more lateral position (Lepidopterous larvae, &c.). A concentration along 
two lines of the body, ventral and lateral, has already commenced in Peripatus. The 
original Protracheate being supposed to have had numerous small tracheae diffused all 
over its body, the question as to their mode of origin again presents itself. The pecu- 
liar form of the tracheal bundles in Peripatus , a number of fine tubes opening into the 
extremity of a single short common duct leading to the exterior of the body, seems to 
give a clue. The tracheae are, very probably, modified cutaneous glands, the homologues 
of those so abundant all over the body in such forms as Bipalium or Hirudo. The 
pumping extension and contraction of the body may well have drawn a very little air, 
to begin with, into the mouths of the ducts ; and this having been found beneficial by 
the ancestor of the Protracheate, further development is easy to imagine. The exact 
mode of development of the tracheae in present forms must be carefully studied ; there 
was no trace of them in the most perfect stage of developing Peripatus which I obtained. 
Prof. Gegenbaur’s f opinion on the position of Peripatus is, that the placing of it 
amongst the worms is not certain, but that, at any rate, it connects ringed worms with 
Arthropods and flat worms. The general result of the present inquiry is to bear out 
Prof. Gegenbaur’s opinion, but points to the connexion of the ringed and flat worms, 
by means of this intermediate step, with three classes only of the Arthropods — the 
Myriopods, Spiders, and Insects, i. e. the Tracheata. From the primitive condition of the 
tracheae in lulus , and the many relations between Peripatus and Scolopendra, it would 
seem that the Myriopods may be most nearly allied to Peripatus, and form a distinct 
branch arising from it, and not passing through Insects. The early three-legged stage 
may turn out as of not so much significance as supposed. If these speculations be 
correct, the Crustacea have a different origin from the Tracheata. Peripatus itself may 
well be placed amongst Prof. Haeckel’s Protracheata; Grube’s term Onychophora 
becomes no more significant than De Blainville’s Malacopoda. Some notions of the 
actual history of the origin of Peripatus itself may be gathered from its development. 
In conclusion I would beg indulgence for the many defects in this paper, due to the 
hurry with which it is written (all available time, almost up to the last moment of our 
* Biologische Studien, p. 491. •)• Grundziige der vergleichenden Anatomie, p. 199. 
5 m 2 
