126 Macieay MenmoriAn Vouume. 
‘04 in diameter in 7. fasczata, derived from these mother cells (PI. x1. fig. 2) are to 
be found here and there scattered through the substance of the testis among the 
developing spermatozoa. By successive divisions accompanied by mitosis these give 
rise to large numbers of cells in which in successive stages the nuclei become reduced 
and the cytoplasm increases somewhat in relative amount. <A stage in this process 
of division is represented in fig. 3. Except in the earliest stages there is no central 
connecting mass or cytophore. This absence of a distinct eytophore agrees with the 
results of Monticelli’s observations on the spermatogenesis of Trematodes in general. 
(“Della spermatogenesi nei Trematodi,” ‘ Bolletino della Societa di Naturalisti in 
Napoli,’ Serie 1, Anno 5°, Vol. 5°, 1891, fase. 2°.) Finally the stage represented in 
fig. 4 is attained in which the Sfermatidia have become formed. Each of those, 
about ‘01mm. in diameter, has a small spherical nucleus (003mm. in diameter) of very 
dense, almost homogeneous, appearance, embedded ina very finely fibrillated cytoplasm, 
the whole having a somewhat irregular (usually more or less pyramidal) shape. In 
the next stage the nucleus of the cell becomes approximated towards one side of the 
cell, and develops a process which projects freely from the surface. This process 
gradually increases in length (figs. 5 to 9) until the whole nucleus assumes the form 
of a slightly curved, pointed rod with its base embedded in the mass of cytoplasm. 
It then becomes drawn out more and more (figs. 10 and 11), and at the same time 
somewhat bent so as to resemble a drawn-out letter S. One end of it—that embedded 
in the eytoplasm—has from the first been thicker than the other, and later on 
presents a distinct rounded swelling, the remainder gradually becoming more and more 
attenuated and increasing greatly in length. The swelling gives rise to the head of 
the spermatozoon. As this approaches maturity the contaimed chromatin comes to 
be arranged in the form of a symmetrically folded thread enclosed in a delicate 
membrane and continuous with the axis of the tail of the spermatozoon. At the 
same time there are developed from the posterior aspect of the head a pair of 
extremely long and slender vibratile cilia by whose vibrations the principal 
movements, if not all the movements, of the spermatozoon are brought about. The 
tail of the ripe spermatozoon is no less than ‘2mm. in length in 7: fasczata and about 
the same in 7. mznor,; the head 0:005 in diameter; the cilia ‘015mm. in length. 
In 7: Dendyi the length (about ‘7mm.) is even greater—about a sixth or so of the 
total length of the animal! The shape of the head varies considerably ; normally it 
is rounded, but it is often found to have an elongate form. In 7. Dendy7 the tail, 
excessively fine at the head end, gradually thickens towards the opposite extremity. 
At this end there is frequently a thin membrane-like expansion or a rounded, finely 
granular mass, in which the extremity of the tail is embedded; this becomes absorbed 
when the spermatozoon is quite mature. Running through the thicker part of the 
tail is a fine spiral line which appears to be formed by the spiral twisting of the 
delicate axial rod of nuclear material. 
