330 Mr. A. Tulk on the Anatomy of Phalangium Opilio. 



is the longest, and the ends of the sht prolonged into slight 

 grooves. 



That direct relation which exists between the development of 

 the respiratory functions and the activity of an animal may be 

 well illustrated in the case of the harvest-spider now before us. 

 *' These long leavers/^ observes one of our old philosophers*, " as 

 I may so call them^ of the legs, having not the advantage of a 

 long end on the other side of the hypomochlion or centers on which 

 the parts of the leggs move, must necessarily require a vast strength 

 to move them, and keep the body ballancM and suspended, in so 

 much, that if we should suppose a man^s body suspended by such 

 a contrivance, an hundred and fifty times the strength of a man 

 would not keep the body from falling on the breast.^' Hence is 

 understood the reason for the large size and dilated character of 

 the tracheal vessels, their principal distribution within the cephalo- 

 thorax, whereunto the locomotive organs and their powerful mus- 

 cles are attached, while two or three tubes alone supply with air 

 the abdomen, in the imperfectly constructed segments of which, 

 little, if any, mobility can exist. In this latter respect insects 

 offer indeed a striking contrast to the Phalangia. 



In concluding these details relative to the anatomy of the Pha- 

 langia, it might be expected that I should offer some remarks 

 upon the rank and position which they hold among other groups 

 of the Arachnida ; but to do so would, I conceive, be to venture 

 upon deductions, to which in the present imperfect state of our 

 knowledge upon the structure of these animals in general, and 

 more especially of the Trachearia, the naturalist is scarcely ca- 

 pable of arriving. For what, it may be asked, is as yet known, 

 or at least, definitively, of the conditions of the internal organs in 

 Galeodes, Chelifer, Pycnogonum, and the numerous tribe oiAcari ? 

 Such considerations, while they suggest to others very interesting 

 points of inquiry, will obviously constrain me for the present to 

 the enunciation of facts alone. 



EXPLANATION OF PLATE V. 



Fig. 26. Female generative organs seen from below, the natural relation of 

 the parts having been slightly disturbed; or, the extremity of the 

 ovipositor projecting from its true sheath of a black colour, and 

 which is surrounded by the muscular sheath ms-, ng, ng, abdo- 

 minal nervous ganglia ; /, fatty mass or liver ; 3, 4, coxae of pos- 

 terior pairs of legs ; D, appendages to second coxal joints. 



Fig. 27. The ovarium and ovisac from above, the latter greatly distended 

 with ova ; o v, the oviduct ; o', detached ova surrounded by their 

 vitelline capsules. 



Fig. 28. The ovipositor detached from its sheath ; twenty only of the annuli 



* Hooke's Micrographia, 1665, obs. 47, of the Shepherd-Spider. 



