422 ME. H. M. BEEIVAKD OK THE CHERISrETID^. 



the nucleus is seen surrounding them in a thick layer. This 

 protoplasmic investment of the tubules gradually fades away as 

 they spread out through the body until it is no longer demon- 

 strable : indeed, the tubules themselves are so fine that they can 

 be seen only with high powers. The tubules from the anterior 

 pair of tracheae run forward, from the posterior pair backward, 

 at least in some cases ; I could discover no anastomosings or 

 branchings among these tubules. 



In addition to these stigmata, there are rudimentary or 

 vestigial stigmata on all the remaining abdominal segments. 

 The claim that stigmata occurred on all the segments was, 

 curiously enough, made so long ago as 1816 by Treviranus *; 

 but, as has been already often pointed out, he mistook the inden- 

 tation of the cuticle caused by the dorso-ventral muscles for 

 stigmata, and claimed them equally for the dorsal and ventral 

 surfaces. The markings which I claim to be vestigial stigmata 

 are much more definite (figs, 1, 2, and 3) ; the last figure repre- 

 sents one of the vestigial stigmata (from fig. 2) magnified 2000 

 times, to show what a definite scar-like mark it is. It appears to 

 be completely closed. That these markings have been over- 

 looked is hardly to be wondered at, as they can be seen only on 

 cleanly macerated specimens with a high (300-500) magnifying 

 power. 



There can, I think, be little doubt that these are indeed vesti- 

 gial stigmata t. Fig. 1 shows how closely in that animal (the 

 Ohisium, sp., from the Thiiringer Wald) they agree, in position 

 and in their relations to the setse, with the functional stigmata. 

 In fig. 2 we find them in quite another position. This difierence 

 in position is exactly what we find in other Arachnids ; in some 

 the stigmata are wide apart, as in Scorpio ; in others {Galeodes) 

 they almost, and sometimes even quite, meet in the ventral 

 middle line. This movement of the stigmata is to be attributed 

 to the change of the position of the blood-sinuses owing to the 

 development of the digesting diverticula. When the diverticula 

 develop so as to leave a median ventral blood-sinus, as in 

 Galeodes, the stigmata also wander towards the middle line. 



■ * Vei-mischte Schriffcen, Bd. i. p. 15, 1816. 



t Had there been only two of these rudimentary markings, i. e. on the two 

 segments following those which have the functional stigmata, no one would 

 have hesitated for a moment to claim them as the homologues of the third and 

 fourth stigmata of Scorpio. 



