376 



PROF. W. J. DAKIN ON THE 



Peripatus arise in bunciies from the bottom of little epidermal 

 pockets 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 tracheje separate off in large or small 

 packets from the main bundle and radiate in different directions. 

 The trachese of these bundles in their turn gradually separate 

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

 the fact tha.t only the larger main bundles are readily visible 

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

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

 this is the appearance when the inner surface of the body- wall is 

 examined. The arrangement is indicated in the illustration 

 (PL II. fig. 6). 



The tracheal pits are arranged somewhat irregularly, but 

 mainly in the manner indicated by Balfour in 1883 in Peripatus 

 cape7isis. There are two irregular rows dorso-laterally on each 

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

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

 fig. 6, N.O.). The more ventral series 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 low next to the longi- 

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

 It is difiicult 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. Gaffron (8) states that there are about 75 per segment 

 in Peripatus edwaixlsi. We have counted over 32 without 

 trouble in segments of our Per ipato ides. 



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. There 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 aperture. 



Branching of the Tracheae. — A great deal of doubt has been 

 expressed as to the course of the traclieas 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 exceptionally." Balfour stated 

 that the tracheae were " extremely minute, unbranched (so far 

 as I could follow them) tubes." Sedgwick, in his article 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 

 Peripatoides^ but if a piece of alimentary canal-wall in the 

 fi-esh state is mounted in salt solution and examined with 



