32Ji Mr. A. Tulk on the Anatomy of Phalangium Opilio. 



repeated examinations of the structure of the above sheath* under 

 the microscope, and that also already alluded to as investing a 

 corresponding part of the male organs, I feel convinced of its 

 muscular texture from having observed that these longitudinal 

 fibrils, which are continuous from one end of it to the other, are 

 composed each of a single row of disc-shaped particles inclosed 

 within a distinct sheath. Some of these may be seen separated 

 like beads from each other, but still connected by their sarcolemma; 

 others lying obliquely upon each other like pieces of money, and 

 when seen directly from their edge in apposition, they give rise 

 to the appearance of the transverse striae. 



The retractor muscles of the ovipositor (PI. V. fig. 26. rm) di- 

 verge slightly from the base of that organ, to which they are at- 

 tached, to be inserted into the penultimate dorsal arc, as in the 

 male. 



In addition to the above organs are two long slender csecal 

 tubes, which lie along the under surface of the muscular sheath 

 of the ovipositor, and contain in their interior a granular sub- 

 stance. They are accompanied each by a delicate tracheal vessel, 

 which winds spirally round and ramifies upon them, and they 

 appear to open into the oviduct upon either side where it is en- 

 tering the ovipositor. From their form and position, these tubes 

 may perhaps be regarded as analogous to the gluten-secretors of 

 insects. 



A considerable degree of interest is attached to the generative 

 organs of P. Opilio in both sexes, from its having been first stated 

 by Geofiroyt, and afterwards by Latreille in his ' Hist. Nat. des 

 Fourm.,^ that this species was merely the female of P. cornutum. 

 In a memoir contained in that work (sur la generation des Fau- 



* Subsequently to receiving the proof sheets of this portion of my paper, 

 I found that 1 was in error with regard to one point in the structure of the 

 muscular sheath of the penis and ovipositor of Phalangium. What I have there 

 described as ultimate fibrils are narrow and elongated fasciculi, which, by 

 the pressure to which they have been submitted in placing them between two 

 slips of glass for examination, have become separated by transverse cleavage 

 into the c?esc-shaped bodies alluded to. If however the surface of these be 

 carefully examined, it is seen to be minutely granular, an appearance pro- 

 duced by the numerous fibrils they contain, each of which is made up by rows 

 of primitive particles or sarcous elements of Bowman, splitting in the direc- 

 tion of the transverse striae. It was owing to my having overlooked this 

 peculiar structure of the discs, the ^-inch power of my microscope being 

 hardly sufficient to define it clearly, that the mistake has arisen. The sar- 

 colemma invests as a delicate membrane these fasciculi, which in this sheath 

 of Phalangium, instead of being aggregated together in bundles to form a 

 solid muscle, as in the legs and other parts, remain distinct from and in 

 parallel apposition with each other, so as to form a hollow tube. 



f Hist. Abreg^e des Insectes, 1762. 



