588 DESCRIPTION OF THE ADULT T&NIA ECHINOCOCCUS. 



the anterior root from the point of the hook is 0*013 to 0*015 mm. ; 

 from the posterior end of the hook, 0*022 to 0'025 mm. 



Behind the four 1 plainly muscular suckers (0*13 mm. in diameter) 

 the head narrows to a neck about 0*25 mm. thick, which then passes 

 without distinct boundary into the unsegmented anterior part of the 

 body. The first segment is but faintly marked off, being scarcely 

 broader than the preceding portion of the body, and almost as long 

 as broad. In the second segment the breadth has been doubled, and 

 the length increased four times, while the male and female reproduc- 

 tive organs can be distinguished a peripheral cirrhus, a vas deferens, 

 and eggs which collect in the uterus in the middle of the joint, and 

 sometimes already exhibit the first signs of embryonic development. 

 The third and last joint exhibits all the characters of maturity. It 

 has not merely grown to be 2 mm. long by 0'6 mm. broad, but is 

 also provided internally with hard-shelled eggs, which enclose the 

 familiar six-hooked embryos, and, according to the computations of 

 Johne and Kiichenineister, are about 500 in number. 2 In isolated 

 eggs one can distinguish, besides the hard shell, also the outer clear 

 egg-membrane, which is so distant that the total diameter is 0'065 mm. 

 The form of the uterus is moderately simple ; one can recognise a 

 wide median stem, with several diverticula or short, slightly ramified 

 lateral branches. In spite of the minuteness of the tape-worm, the 

 eggs have the ordinary size, but the shell is comparatively thin, and 

 is but faintly granulated on the outer surface. The internal space is 

 oval, and has a transverse diameter of from 0*03 to 0'027 mm. The 

 cirrhus of the ripe joint is usually directed to the opposite side from 

 that of the preceding, so that Tcenia echinococcus agrees with the other 

 cystic tape-worms in the irregularly alternating arrangement of the 

 generative openings. 



Before this last ripe joint is liberated, a new joint appears; so 

 that for a while four proglottides are distinguishable, instead of three. 



The calcareous corpuscles are somewhat large, and, in the more 

 transparent anterior part of the body, are easily found. In fresh 

 specimens the course of the vessels can usually be seen very beauti- 

 fully. Von Siebold even mentions the ciliation which is observable 

 in the anterior of the body-parenchyma, behind the suckers, at the 

 sides of the neck and body. 3 



1 Von Siebold once saw a T. echinococcus with six suckers (loc. cit., p. 425). Nothing 

 was noted as to the structure of the segmented body. The fact that this malformation has 

 been seen only in one specimen is in favour of the opinion we previously expressed as to 

 its spontaneous origin. 



2 My previous estimate (4000 to 5000) is too high. 



8 Two memoirs, which have appeared while these sheets were passing through the 

 press, establish beyond cavil the repeatedly denied existence of a ciliary apparatus in the 



