T7ENIA SOLIUM. 309 



trates gradually into the interior of the whole 22, 24, 26, or 28 

 hook-sacs of our Tania, between these and the hooks, and may 

 perhaps, when collected in very great abundance, elevate the 

 hooks and finally push them out altogether. I cannot state 

 whether this, as is usually said, is a mere indication of age, or 

 whether it may not also take place in consequence of a hyper- 

 genesis of the pigment itself, without being connected with age. 

 Moreover, we must not forget that a great number of the cases 

 in which the falling out of the hooks by age is mentioned, are to 

 be attributed to the fresh heads having remained too long in 

 water or in the evacuations, or to decompositions when the dis- 

 sections have been made after a considerable interval. Placing 

 them in too-concentrated spirit, in time causes the hooks to 

 leave their sacs. Virchow states that the pigment is molecular, 

 granular ; sometimes, on the front of the head, crystalline, and 

 like melanine ; and that it is sometimes also imbedded in vesicles. 

 I have also sometimes thought that I have found such crystals, both 

 in mature Tanice and in Cysticercus cellulosce, even that of the pig. 



The hook-sacs, which, as well as the hooks, are placed in a 

 double circular series, may be best compared, as to form, with 

 the beaker-glasses of the chemists. Even when the hooks have 

 fallen out, they are very distinct.lv visible, from their black 

 coloration by the pigment. Their length corresponds pretty 

 exactlv with that of the stems of the hooks in both series. 

 Their breadth for the first series is, in the middle, 0*021 — 28'" = 

 0-017 — 0-063 millim.; for the second series, 0-017 — 21"' = 

 0-039 — 0-047 millim. For the base of the first series, 0010 — 

 0-017"' = 0-0.23— 0-039 millim. ; and for that of the second, 

 0-010'" = 0023 millim. 



The upper orifices, through which the stems of the hooks issue, 

 measure, in the first series, about 0-010— 0017'" = 0023 — 

 0029 millim. in length ; and 007 — 0-010'" = 0019— 0023 

 millim. in breadth. Those of the second series do not appear to 

 differ greatly from this, but are more difficult to measure, from 

 their greater softness. 



In number and position the hooks correspond with the sacs 

 just mentioned. As in all Tcenice, the points of all the hooks 

 fall in the same circle ; their spines, which appear to act in the 

 manner of hypomochlia, also fall nearly in a common circle, or, 

 at the utmost, in two circles lying very close together; the roots 



