26 Mr. H. M. Bernard on the Origin of the 



I cannot pretend to solve. It may perhaps be referred to the 

 force of heredity coming into action as soon as the animal is 

 more or less withdrawn from the struggle for existence, as a 

 pupa may almost be said to be when encased in a cocoon. 



(B) In order to get more light on the homologies of the 

 ventral row of structures in tlie Arachnids which I propose 

 also to refer to a row of setiparous glands, I have naturally 

 turned my attention to some of the less known orders. A 

 small Chernetid, apparently an Obisium, has yielded me 

 unexpected results. 



The stigmata of the tubular trachese on the second and 

 third abdominal segments are followed by a complete row of 

 segmental apertures running along each side to the end of the 

 ahdomen. Their position corresponds exactly with those of 

 the stigmata, and I think it is impossible to doubt that they 

 are homologous with these latter. In this interesting Arachnid, 

 then, there are nine pairs of apertures on the nine posterior 

 abdominal segments. The two anterior pairs are stigmata. 

 The function of the other seven, for want of sufficient 

 material, I have not yet made out. It is well known that the 

 Chernetidse spin webs, and there seems to be no very clear 

 idea where the glands are situated. Croneberg's claim * that 

 the spinning-gland opens on the mandibles is probably correct. 

 I find a very distinct aperture on a small prominence behind 

 the point of the movable piece of the mandibles. In that 

 case these '' stigmata " may be purely rudimentary and 

 functionless. If, on the other hand, these seven pairs of 

 apertures following on, and evidently homologous with, 

 stigmata prove to be the openings of spinning-glands (a point 

 I hope soon to investigate), we should have a remarkable con- 

 firmation of my suggestion that the lung-books or tracheee 

 and the spinning-glands of the Araneids are homologous 

 structures as common derivatives from setiparous glands. 

 We learn also from these ?2z*??e pairs of abdominal apertures in 

 Obisium that the limitation of the number of stigmata in 

 Scorpio is not original, i. e. inherited from a Limulas 

 ancestor, but is due to a secondary reduction of what were 

 originally segmental structures along the whole abdomen. 



(4) The coxal gland of Galeodes opens, as Sturany f 

 suspected, between the third and fourth appendages, i. e. on 

 the coxa of the first leg. Dufour, who mistook it for a sali- 



* " Beitrac^ zur Kenutuiss des Banes cler Pseudoscorpione," Bull. Soc. 

 Imp. Nat. de'Moscou, t. ii. (1888). 



t " Die Coxaldrusen der Arachnoiden," Arb. Zool. Inst. Wien, t. ix. 

 (1891). 



