376 PROF. W. J. DAKIN ON THE 



Peripatus arise in bunches from the bottom of little epidermal 

 pookets which may be termed stigmata or tracheal pits. For a 

 varying distance the delicate tracheal tubes run in a bundle all 

 more or less parallel to each other and without branching ; 

 gradually, however, the tracheae separate off in large or small 

 packets from the main bundle and radiate in diflerent directions. 

 The trachea3 of these bundles in their turn gi'adually separate 

 until they run alone. As a consequence of this arrangement and 

 the fact that only the larger main bundles are readily visible 

 even wlien filled with air, each tracheal pit appears to give rise 

 to a little irregular rosette or star of trachese. That is to say, 

 this is the appeai-ance when the inner surface of the body- wall is 

 examined. The arrangement is indicated in the illustration 

 (PI. II. fig. 6). 



The tracheal pits are arranged somewhat irregularly, bvit 

 mainly in the manner indicated by Balfour in 1883 in Peripatus 

 capensis. There are two irregular rows dorso-laterally on each 

 side, that is in the quadrants between tlie heart (PI. II. 

 fig. 6, Ht.) (mid-dorsal line) and each longitudinal nerve (PI. II. 

 fig. 6, N.C). The more ventral sei'ies on each side appears to 

 comprise the larger bundles. On the ventral surface there are 

 also four longitudinal series of tracheal pits, two to each side of 

 the mid-ventral line (only two series, those to the left of the mid- 

 ventral line, are shown in fig. 6). The row next to the longi- 

 tudinal nerve on each side appears to comprise the larger bundles. 

 It is difficult to say how many tracheal pits there are to a segment, 

 for the number appears to vary, and the smallest ones are not 

 easily seen. No attempt has been made to determine the full 

 number. Gaflt'ron (8) states that there ai'e about 75 per segment 

 in Peripatus echvardsi. We have counted over 32 without 

 trouble in segments of our Peripatoides. 



There are some very large tracheal bundles in the head, supply- 

 ing the large nerve ganglia. Some of the largest of these arise 

 ventrally, and there seems to be a series of tracheal pits sur- 

 rounding the mouth-opening. Just behind the mouth there is a 

 large pit in the mid-ventral line. Thei'C are also large pits 

 ventrally placed and in the median line in front of the mouth. 

 Other large pits occur to the sides of the oral apei'ture. 



BrancMng of the Trachece. — A great deal of doubt has been 

 expressed as to the course of the trachete in Peripatus. Thus, 

 in Balfour's treatise on the Anatomy and Development of 

 P. capensis (1), the following statement occurs: " Moseley states 

 that the tracheae branch, but only exce))tionally." lialfour stated 

 that the trachese were " extremely miiuite, unbranched (so fai' 

 as I could follow them) tubes." Sedgwick, in his ai'ticle in the 

 Cambridge Natural History (10), states that the tracheae " appear 

 to branch but only exceptionally." 



Now the main trunks do not branch in the West Australian 

 Perijxctoides, but if a piece of alimentary canal-wall in the 

 fresh sto.te is mounted in salt solution and exa.mined with 



