J. Johnstone 
411 
of the degeneration of the testes, the vasa efferentia, vas deferens, and 
vitellaria. PI. XXIV is based on a reconstruction of a mature segment 
from serial sections: the segment was one which was still a part of the 
strobila. The proglottis still continues to increase in size after de¬ 
hiscence from the strobila., and I have no doubt, though I have not made 
sections from such a free proglottis, that the progressive degeneration 
of all the organs other than the uterus still proceeds while the segment 
is free within the alimentary canal of the host, or even lying freely on 
the sea bottom. 
The uterus is the seat of the principal changes accompanying 
maturation. Originally a cylindrical straight tube of no great diameter 
it continues to increase in diameter as it becomes filled with fertilised 
eggs, until it occupies by far the greater part of the volume of the 
proglottis in front of the genital papilla. Originally its walls consisted 
of a cuticular membrane lined internally with a single layer of nuclei, and 
externally with several layers of cells, but in the matiu'e phase it becomes 
a very thin membrane which bears internally and externally widely 
separated nuclei. The expansion of the uterus is brought about by the 
formation of the lateral evaginations of its wall and then these flatten out, 
or fuse together. The contained embryos are about 0'04 mm. in diameter 
and each has a very distinct cell membrane and contains a small number 
of cells embedded in a granular matrix. The embryonic hooks are not 
present—that is the oncosphere stage is not attained while the embryos 
are still within the proglottis, at least not in the stage while the 
developing segment still forms part of the parent strobila. 
A “birth-pore” is probably not formed in the proglottis of Tetra- 
rhynchus erinaceus and the embryos are only liberated from the proglottis 
when the latter undergoes dissolution. Nevertheless a birth-pore may 
possibly be formed at a later stage than I have been able to study, for 
such an opening is certainly present in the proglottides of the allied 
species Tetrarhynchus tetrabothrius. When a ripe segment of the latter 
worm is observed closely—the strobila lying in fresh water—the 
extrusion of the eggs may be seen, especially if after immersion in fresh 
water the worm is put into weak formalin. The eggs appear to issue 
from the dorsal or ventral surface of the proglottis and sometimes it 
appears as if they came from the genital opening ; but I suspect that in 
the latter case the opening breaks through near to the genital papilla. 
The birth-pore does not appear to be constant in position, and it is 
probably formed where the wall of the proglottis is thinnest: it is a 
purely secondary structure and not a true uterine pore. I would refer 
27—2 
V 
