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Show 1895.] HYDBACHNID POUND IK COENWALL. 193 lobes by the swelling and rounding of its dorsal and lateral surfaces both anteriorly and posteriorly, leaving a thinner and narrower portion between, but without any breach of continuity or line of demarcation; the whole forms one piece. The mass varies a good deal in form in different specimens, and even the two sides of the same individual are seldom quite similar, but the general shape always corresponds fairly well. The masses on the two sides of the body are a short distance apart anteriorly, but approach each other closely posteriorly; almost at their hinder ends they are joined by a short bridge (fig. 17) quite continuous with both sides, so that the organ on both sides of the body forms one unbroken whole. From the ventral surface of the narrower part of the testicular mass on each side proceeds a vas deferens of moderate length, which runs upward and forward. At its anterior (distal) end, which is nearest to the dorsum, this vas deferens joins its fellow from the opposite side of the body, and the two enter a short widish ductus ejaculatorius (figs. 17, 18, 23, de.) with very fleshy walls, which runs downward and a little forward. This organ is inversely pyriform, being narrowed at its distal end so as to discharge by quite a small opening into a very large penial canal (figs. 18, 23, pc), which again is inversely pyriform, its largest part being near to where the ductus ejaculatorius enters ; this canal proceeds almost perpendicularly downward. On the outside of the widest part of the canal is a chitinous bar (fig. 18, cb.), from which a series of diagonal muscles (fig. 18, mc.) spread out; so that those on the two sides of the body, acting simultaneous^, would form powerful compressors. Longitudinal muscles also run from the ductus ejaculatorius to the inner side of the cuticle of the body close to the genital opening; thus the penial canal can be compressed longitudinally as well as transversely. The canal itself is a large, membranous, tubular organ, considerably and irregularly folded, so that the portion nearest to the ductus ejaculatorius is apt to form a series of pouches, and the more distal part a number of longitudinal folds converging to the genital aperture. This last-named part is not much hidden by muscles when the organ is dissected out, whereas the more bulbous proximal portion is almost surrounded by them. I have not been able to discover any chitinous penis such as Croneberg draws in Trombidium. The penial canal, as I have drawn and described it, is as at rest under ordinary conditions. I have not been able to examine it at the moment of coition, and therefore 1 a m not able to say whether the membranous tube is evaginated-thus, in effect, forming a penis, which seems very probable,-or whether the sperm is simply deposited on the exterior of the female, or conveyed by the feet as observed by Koenike in Curvipes fuscatus. The testicular mass appears to be one solid block (subject to the foregoing description of its shape), and there is not any line of demarcation or any membrane or division between its various parts; but still it is not really so. The greater part of it has an external coating of a single layer of large cells about -015 m m . in diameter, P B O C ZOOL. Soc-1895, N o . XIII. 13 |
