4 Mr. F. G. Penrose on a Cysticercus 
The cuticle of the tails and of the posterior part of the ante- 
rior extremities is thrown into a number of irregular trans- 
verse wrinkles. These have no relation with the segments of 
a Tenia, though sometimes curiously simulating them and, 
as Dr. Monier has shown, are due to the following cause :— 
The tail consists of a central core enclosed within the mus- 
cular zone, which contains both circular and longitudinal 
fibres, the latter greatly predominating ; and between this 
layer and the cuticle there is a loose, subcuticular, very actively 
growing connective layer of cells. 
As the central core increases but slowly relatively to this 
outer layer, and is of a firmer tissue, supported and enclosed by 
the muscles, it necessarily follows that the cuticle will be 
thrown into folds by the rapid increase of the subcuticular 
layer. 
At the posterior extremity of the tail there is generally, 
though not always, a slight depression (vide figs. 1, 2, 3), 
looking something like the one at the anterior extremity. It 
seems to have nothing to do with any internal canal, as 
Monier says that both he and Leuckart have searched in vain 
for any canal that opened externally there; and although I 
made several series of sections expressly to try and find one, 
I did not succeed. Monier observed that whilst the larval C. 
pistiformes were still in the liver of their host, on the twenty- 
second day after infection, several specimens, though not all, 
became constricted somewhere near their middle, and two 
semiequal portions were formed, connected by a twisted cord, 
each end of which fitted into a depression, the one at the 
posterior extremity of the anterior part, the other at the ante- 
rior extremity of the posterior part (doc. c7t. chap. il. p. 26, and 
pl.i. fig. 3). The posterior extremity was thrown off, and the 
anterior part retained simply the depression into which the 
cord fitted ; but occasionally there was a short remnant of the 
connecting cord left in the form of a short tag. 
In the present form I have never seen the tag. Although 
the shortest specimens almost invariably show the depression, 
it is equally well marked in some of the longest, though 
depressionless ones have perhaps a greater average length 
than the average of the whole number ; but those without a 
depression are decidedly exceptional. So I do not think 
that the great difference in length is due to some not becoming 
constricted and retaining their whole original length whilst 
others have lost their posterior halves, both from what has 
been said above and also because between the shortest and 
longest there is a perfect gradation in length. 
In the exception (fig. 4) mentioned above, the anterior 
