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Show 204 DR. T. S. C O B B O L D O N ENTOZOA. [Feb. 1, as to size and contour. These I believe to be due to respective degrees of growth (fig. 5). Selecting one of the largest hooks, I found it to measure about -g^ in. in length, the broadest part of its posterior root-process giving TAny hi. approximately. The base between the two fang-points measured -^hi m* > whilst internally the hook displayed a well-defined cavity taking the general form of the organ itself. At its lowermost angle the cavity becomes suddenly narrowed into a fine channel that terminates in an opening at the centre of the extremity of the posterior fang, This tube is something less than the TTJOTTTJ m c n m diameter (fig. 6). By making a vertical section of the worm one may obtain a good veiw of the arrangement of the parts about the head. Somewhat diagrammatically I have represented the parts as they appear in the retracted condition of the proboscis (fig. 7). This organ is now seen resting, as it were, in a cavity formed by the arching over of the rosette-shaped collar. The sheath of the proboscis itself is bordered by powerful retractor muscles, which during extreme contraction reduce the proboscis to the form of an oval disk, at the same time carrying the whole organ downward so as to conceal it entirely within the lumen of the neck. The lower end of the muscular sheath assumes the shape of a reversed cone, well rounded off at its dependent apex. The sides of the neck are lined with longitudinal muscular bundles, portions of which are, I suspect, differentiated to form the special retractors of the sheath. Be that as it may, on either side of the bulbous end of the sheath the lemnisci are conspicuous and easily drawn out with a fine pair of forceps. They extend downwards to near the centre of the somatic cavity, attaining, in the largest specimens, a length of no less than f inch. Free ovaria were not observed; but 1 found abundance of eggs, which were of an oval form, measuring about 3-^- in. from pole to pole and -gAjjin.in breadth. They displayed three distinct envelopes. The outer transparent and very delicate membrane was marked by decussating curvilinear lines (fig. 8 a), being succeeded by a second thicker envelope (b), the two being separated by fluid contents. Many ova were found freed from these coverings, these being, as a rule, rather more advanced in growth, as shown by their finely divided yolk-contents, which in some instances had passed into an early embryonal stage. In this condition the eggs measured only ^ by -^ in. My sections of the body of the parasite showed the openings of numerous water-vascular channels; but I did not carry the investigation further. EXPLANATION OF PLATE XVI. Fig. 1. Four examples of Echinorhynchus elegans: a, immature; b, c, d, full-grown, natural size. F"ig. 2. Anterior extremity of a mature worm, showing the annulations of the neck (a), the collar in profile (b), and the exserted portion of the proboscis (c). Enlarged. Fig. 3. The collar, viewed from above, showing the folded border of the neck (a), the series of rays (b), and the central opening (c). Highly magnified. Fig. 4. Diagram of the proboscis in its retracted condition, to show th?arrangement of the hooks. |
