412 
Tetrarhynclms erinaceus 
here to Braun (1894-1900, pp. 1438-1451) for a discussion of the 
morphological significance of this opening in Cestodes generally. 
I describe very briefly the principal changes which take place as 
the proglottis passes from the immature to the sexually mature 
condition. 
Testes and ducts. The testicular follicles degenerate completely in 
the ripe proglottis. In stages a little younger than that represented in 
PI. XXIV the testes are restricted to a very narrow zone between the 
layer of vitellaria and the wall of the uterus, and even here they may 
be present as a layer of only one or . two follicles in depth. Some are 
also present at the exti’emities of the segment. In older segments such 
as that represented in PI. XXIV the marginal testes degenerate com¬ 
pletely and there are only a few left at the ends of the proglottis. The 
few that remain at the anterior end of the segment degenerate later on, 
and in the oldest proglottides that I have sectioned there are only 
a few testes in the part of the segment behind the ovary. In these 
later stages, the testicular follicle becomes much smaller than in the 
early phases, and also becomes spherical in shape. The distal end of 
the vas deferens persists in the oldest segments that I have seen, but it 
becomes relatively shoi’t, the convolutions of the tube become smoothed 
out, and its calibre diminishes. Till the end, however, it still contains 
ripe spermatozoa. 
The vagina. This canal is more voluminous and more richly 
convoluted in the ripe than in the unripe proglottides; and the 
proximal part described as the receptaculum seminis is greatly enlarged. 
Throughout its entire length the vagina is filled with spermatozoa in 
the later stages of the segment. Its relations to the ovary and oviduct 
are the same as in the earlier stages. 
The vitellaria. These glands undergo great reduction as the 
segment enlarges. All those which were present in the peripheral 
regions of the proglottis external to the uterus practically disappear and 
only a few persist at the posterior end of the segment, lateral and 
posterior to the ovary, and the terminal parts of the ducts also persist 
here as the yolk reservoir. In front of the genital papilla the body wall 
becomes very thin and consists only of the integumentary tissues and some 
remains of the vitellaria. Dorsally and ventrally the wall is thinnest and 
it is here that a birth-pore would most easily be formed. 
Further investigation is, of course, necessary in order that the 
complete life history of our Cestode may be elucidated. It is first of 
all essential that the true larval host should be found: this, as I have 
