204 DR. T. S. COBBOLD ON ENTOZOA. [Feb. I, 



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 ^^ in. in length, the broadest part of its 

 posterior root-process giving y"oVo in. approximately. The base be- 

 tween the two fang-points measured -g-i^ in. ; 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 some- 

 thing less than the xochhT mcn 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 re- 

 duce 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 depen- 

 dent apex. The sides of the neck are lined with longitudinal mus- 

 cular 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 down- 

 wards to near the centre of the somatic cavity, attaining, in the 

 largest specimens, a length of no less than | inch. Free ovaria were 

 not observed ; but 1 found abundance of eggs, which were of an oval 

 form, measuring about -g-l-jj in. from pole to pole and ^-Jj-jjin. 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 y4- by -^-q in. My sections of 

 the body of the parasite showed the openings of numerous water-vas- 

 cular channels ; but I did not carry the investigation further. 



EXPLANATION OF PLATE XVI. 



Fig. 1. Four examples of Echinorhyiichus deguns: a, immature; b, c, d, full- 

 grown, natural size. 



Fig. 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 pro- 

 boscis (c). Enlarged. 



Fig. .*'>. The collar, viewed from above, showing the folded border of tbe neck (a), 

 the series of rays (b), and the central opening (c). Highly magnified. 



Fig. 4. Diagram of the proboscis in its retracted condition, I" show thearrange- 

 ment of the hooks. 



