of Tracheary Arachnidans. 49 



are sent off into each of the eight legs, but upon this point I am 

 unable to come to any decided conclusion, and indeed the course 

 of the alimentary tract has eluded all my attempts to demonstrate 

 it with satisfaction. Just before its termination in the anus 

 however, which occupies the posterior extremity of the abdomen 

 (fig. 2 d), the rectum would appear to receive two long csecal tubes 

 (fig.2z); these contain a white opake substance, and maybe traced 

 forwards one on either side of the body till they terminate by 

 entering the first joint of the anterior pair of legs. They must, I 

 conceive, be referred to a biliary, or perhaps more correctly to a 

 urinary system. 



Respiration is effected by means of a system of tracheae 

 (fig. 2 e, e, e) which originate at each side in a minute spiracular 

 orifice (fig. 2/) occupying a latero- dorsal position at the anterior 

 extremity of the abdomen. From the spiracles the trachese pass 

 off, some forwards into the cephalothorax and others backwards 

 into the abdomen ; the former sending branches to the legs and 

 oral apparatus, and to the other organs in the anterior part of 

 the body, while the latter are distributed to the organs of the 

 abdomen. 



One great transverse trunk (fig. 2 g) passes across the posterior 

 part of the cephalothorax, uniting the tracheary systems of op- 

 posite sides. 



The structure of the tracheae (fig. 8) is very similar to that of 

 the same organs in insects ; the spiral fibre however demands a 

 much higher power in order to be rendered visible than is required 

 for this purpose in the generality of true insects. 



There is no part of the internal anatomy of Halarachne more 

 easily demonstrated than the great central nervous mass. This 

 (fig. 2 h) occupies a position near the middle of the cephalo- 

 thorax, and would seem to lie beneath the alimentary canal. It 

 is of a somewhat stellate figure, the margins being prolonged 

 on each side into two pyriform lobes giving off from their apices 

 nervous cords which run to the intervals between the first and 

 second, and second and third pairs of legs. The lateral lobes differ 

 in structure and colour from the rest of the nervous mass, and 

 are visible through the integument without any dissection. No 

 special organs of sense can be detected*. 



The generative system is very obscure. Extending transversely 



* The only other view which it is possible to take of the organ here de- 

 scribed as a central nervous mass, is that which would represent it as a ven- 

 tricular cavity with lateral prolongations. Such view however I believe a 

 careful examination will prove to be untenable, and convince us that it is 

 really to be referred to the nervous system, and results from the confluence 

 of two or more pairs of ganglia. 



Ann. fy Mag. N. Hist. Vol. xx. 4 



