330 DE, W. CARMICHAEL M'lNTOSH ON THE STRUCTURE OF THE 



within the former, and to whose presence the independent wrinkles of the inner 

 structures are due. The longitudinal layer [to) is innermost, and forms a kind 

 of spindle-shaped arrangement ; the anterior fibres — commencing with the ejacu- 

 latory duct (of which they form the special wall) — soon spread out to cover the 

 dilated cavity of the reservoir, then become narrowed as they surround the channel 

 of communication, and proceeding backwards, merge into the longitudinal coat 

 of the posterior chamber. In some positions, these fibres assume a crossed or 

 spiral aspect in the channel of communication ; but, as in the case of the gan- 

 glionic region of the proboscis, this is purely accidental. The margins of the reser- 

 voir and the channel of communication are marked under pressure by the ends of 

 muscular fasciculi, especially posteriorly; an appearance due to the doubling of the 

 looped fibres, but also partly to the presence of the thin circular coat, which lies 

 without the longitudinal. By the contraction of these various fibres, the chamber of 

 the reservoir is squeezed with great force in every direction, like a thick caoutchouc 

 ball or globular syringe in the hand. Its transverse diameter is lessened, and 

 still more, its antero-posterior, while a jet of the minutely granular fluid is squirted 

 into the anterior chamber ; and, in spasmodic efforts, even a prolapsus of its glan- 

 dular lining occurs. In contraction, the entire region is much shortened, and 

 the mass of the looping muscle increased posteriorly. Not only does the peculiar 

 looping of the fibres cause most powerful squeezing of the cavity, but the posterior 

 aperture has a tendency to be closed, and slightly carried forwards, the anterior 

 being less subject to interference. The closing of the posterior aperture (channel 

 of communication) is also greatly assisted by the circular fibres which are situated 

 outside the longitudinal. The varying conditions of the reservoir may be under- 

 stood by comparing Plate IX. fig. 3 with Plate XII. fig. 9, the former show- 

 ing the organ in its ordinary state, the latter in a somewhat contracted con- 

 dition. 



The peculiar looping of the fibres of the reservoir causes a transverse section 

 through its posterior part (Plate IX. fig. 10) to assume a finely radiated spiral 

 arrangement, the whole reminding one strongly of Dr Pettigrew's beautiful 

 diagrams of the arrangement of the muscular fibres of the heart ; and in this case 

 no better structure could have been devised for the complete and forcible evacua- 

 tion of the chamber. Professor Keferstein describes only oblique and longitu- 

 dinal muscular fibres in this region. 



Posterior Region. — Behind the translucent region just described, the opaque 

 white long posterior chamber (C) (intestin, Quatref., Drusentheils of the Germans) 

 occurs. It communicates with the reservoir in front, as previously mentioned, 

 but its posterior end is csecal. The contractile nature of the parts renders com- 

 parison uncertain, but it is generally not much shorter than the anterior chamber 

 in the perfect animal. Sometimes, indeed, it exceeds the latter chamber in 

 length, the simpler structure of its walls giving greater extensibility. In young 



