Haswett—A Monograph of the Temnocephalee. 127 
From the mode of development described above it follows that not only is the 
chromatin of the head of the spermatozoon derived from the nucleus, but also an axial 
fibre in the tail. A somewhat similar elongation of the nucleus is described by Jensen 
as taking place in Plagzostoma vittatum.* 
In the main features of their spermatogenesis there appears to be a general 
agreement between the Monogenetic Trematodes and the Rhabdocceles ; and in these 
main features Zemnocephala agrees with both. In all a rounded mass of cells— 
sperm-morula, or spermatogemma—is formed by mitotic division of the primitive 
cell. In some cases—Plagzostomide and some Monogenea—these are connected with 
a central nucleated or non-nucleated mass or cytophore ; in other cases this is absent, 
and the mass of cells contains a central space. In each of these cells—spermatocytes 
becoming spermatidia—it is the nucleus that plays the important role in the formation 
of the spermatozoon—the cytoplasm forming a thin investment, together with any 
appendages that may be present. The precise way in which the nucleus becomes 
modified to form the main part of the spermatozoon varies, however, very widely ; 
and its history as we trace it in 7emnocephala is highly characteristic, and differs 
considerably from anything that has been observed in either group.t 
XIII.—Femare Repropuctrive Oreans. 
These consist of ovary, receptaculum seminis (or, better, receptaculum vitelli), 
oviduct, uterus, vagina, vitellime and shell-glands, together with the unicellular 
glands already described as opening on the ventral surface around the genital 
opening. 
The ovary (Pl. xiv. fig. 2, ov. ; Pl. xv. figs. 1 and 2, 0.)f is an oval body about 
‘15 to ‘25 mm. in length, situated on the right of the median line, with its long axis 
directed obliquely. It consists of a solid mass of ova enclosed in a capsule of 
muscular fibres, the ova towards the right-hand end being small, polygonal and 
immature, those at the left extremity being fully mature. Each ovum, with the 
exception of those at the right end, is a narrow pyramid about -083 mm. in length, 
passing transversely through the entire thickness of the ovary. The protoplasm 
contains a few spherical brightly refracting particles and a large nucleus, in which, in 
the living condition, streaming movements were observed to take place. 
* ** Recherches sur la Spermatogenése.” ‘Arch, de Biologie,’ IV. (1883). 
t Vide v. Graff, /.c. p. 156; Bohmig, /.c. p. 286; Wright and Macallum, /.c. p. 38; Braun, /.c. p. 470; Jensen, 
‘Recherches sur la Spermatogenése,” ‘ Arch de Biol.’ IV. (1883) ; Monticelli, ‘‘ Della Spermatogenesi nei Trematodi,” 
‘ Bolletino della Societa di Naturalisti in Napoli,’ Vol. 5° (1891). 
$ See also former paper, Pl. xxu. fig. 11. 
