THE ANATOMY OF PENTASTOMUM TERETIUSOULUM. 51 



and testis wall, slanting upwards and forwards as it does so 

 (fig. 68_, G.). A similar double ridge is attached to the 

 roof of the chamber above mentioned, and this ridge again 

 terminates in two papillee, each with a funnel-shaped opening 

 — the anterior termination of the tubes leading from the 

 testis cavity (fig. 17, V. S. 0.). Thus in transverse sections 

 the latter is seen to be continued forwards and above the 

 efferent ducts, whilst that of the common seminal chamber 

 passes backwards and beneath the ducts (fig. 68, F. G.). 

 There is around the ducts a strong development of dis- 

 tinctly striated muscles, the ducts themselves having a thick 

 cellular wall. 



Along its whole course the testis is attached to the mid- 

 dorsal line of the body-wall by a thin mesentery, and it is in- 

 teresting to note that just at the very anterior end, where the 

 two tubes above described lead out from the cavity, this mesen- 

 tery becomes double (fig. 17, Mes.). It might have been ex- 

 pected that, as in P. protelis, one of these mesenteries would 

 have passed on to each of the vesiculse, but such is not the 

 case, and the latter have no supporting structures of this 

 nature. The presence of this double communication between 

 the cavities of the testis and vesiculae, which has now been 

 described in P. protelis, P. proboscideum, and P. tereti- 

 u senium, together with the double nature of the testis for 

 the greater part of its length in P. taenioides, indicates that 

 originally the testis in Pentastomum was a paired structure, 

 as it is at the present time in certain other Arthropoda, such 

 as the Aranea. 



{b) Vesiculse seminales. — This portion of the repro- 

 ductive organs is very well developed in P. teretiusculum, 

 and of considerable length (fig. 6). It has the form of a tube 

 bent double upon itself, the upper half running backwards 

 and downwards, the lower half forwards and slightly down- 

 wards. It has the same relationship to the hook-gland as the 

 ovary has, and in early stages (fig. 18, V. S.), when the tube is 

 a comparatively small one, the upper half is seen to pass down- 

 wards right through the middle of the gland. The same feature 



