510 MR. A. D. MICHAEL ON THE 



are inserted. From the posterior edge of the plate arises a series of fine constrictor 

 muscles (mc), which pass round the outside of the penial canal. The other principal 

 muscles connected with this part of the canal are a pair of central retractor muscles 

 (mr^) inserted into the median posterior line of the lower part of the organ, and a 

 network of constrictor muscles which completely envelop the upper end of the organ 

 like a cap ; these are not shown in the drawing, as they would entirely hide that portion 

 of the canal. The glandular antechamhers (vg) enter the upper end of the jienial 

 canal as hefore stated, passing through this muscular layer. The outer portion of the 

 l^enial canal (pc~) lies entirely ventral to the amphioid sclerite, and is a membranous 

 structure somewhat wider than the inner portion (pc^), hut its exact Avidth and form 

 depend on the amount of the retraction of the organ for the moment. It forms a thin- 

 walled flexible chamber connecting the inner part of the penial canal with the great 

 external labia (/<?). 



The penial canal presents internally a complicated series of folds of a thin flexible 

 membrane, which is marked in most parts by a very fine series of parallel, wavy, linear 

 ridges, projecting considerably in parts ; in other places the membrane is provided with 

 very fine spines or hairs, some of which form two paired brushes (fig. 21, bh). When 

 sections taken through the edge of the external genital aperture are carefully examined, 

 it will be seen that this membrane is really an invagination of the exterior cuticle of 

 the body, and retains its character of the wavy parallel ridges ; but both membrane 

 and ridges have become very much finer and more delicate than on the exterior 

 of the creature. It would be hopeless to describe or even to draw the whole of 

 the complicated series of folds into which this membrane is thrown, nor are they by 

 any means always similar in different specimens ; but the main features are generally 

 preserved, and something of them may be gathered from the figures and something 

 respecting them may be said here. First, the membrane folds so as to divide the 

 upper end of the penial canal, which is enlarged in some species, into three lobes or 

 chambers communicating and forming a kind of trefoil ; below this the membrane folds 

 in and forms a very narrow constriction ; below this again it appears to be invaginated 

 more than once, and to form various folds and recesses ; but if it be looked at from 

 behind after its outer walls have been cut open and separated, it will be seen that there 

 is an arrangement in the central line which is depicted in figs. 21, 34 ; there is a longish, 

 very hyaline, and thin-walled central tube, which is slightly sigmoid in form, but looks 

 straight when seen from the front or rear, down the middle of the exterior of which 

 tube sometimes runs a slight ridge, the thickness of which varies in different j)arts ; this 

 ridge, when present, is a mere folding together of the two sides of the tube when it is 

 slightly flattened. The lower end of the tube is strengthened by two very small, paired, 

 chitinous, slightly undulated rods, each of which supports a small rounded membranous 

 flap or lobe (mfp) marked with wavy ridges ; each of these flaps ap^iears a mere line 

 when looked at from the anterior, but like a rounded lobe when seen from the side; 

 each flap bears a well-developed chitinous hook, standing slightly upward. Between 

 these rods is a funnel-shaped piece {jie), very slightly chitinized at its open enlarged 

 end, which is the upjier, but hyaline at its smaller end, which is tubular. I have 

 never had the good fortune to obtain Bclella iu copula, or with the j^enial 



