NOTES ON THE HIST1UOBDELLID.E. 
207 
chitinous pieces with elaborate articulations enter into its 
composition. It is thus a much more complex structure than 
the mastax of certain Rotifers to which 1 have compared it. 
Yet the resemblances to the ^‘malleate^’ form of mastax are 
very striking, and are worthy of notice in connection Avith the 
question of the phytogeny of the Histriobdellida?. 
Compared with the typical malleate mastax, as we find it 
exemplified in Brachionus, the jaw-apparatus of Stratio- 
drilus is found to differ in the following chief points : 
(1) The fidcrum is produced into a long slender rod. 
(2) Each ramus is .represented by four more or less 
parallel jointed rods' or ramules, each of Avhich bears 
terminally one of the four complex teeth which represent the 
uncus. 
(3) The uncus is thus essentially related, not to the manu- 
brium, but to the ramus. 
(4) The manubrium is probably represented by a very 
slender rod which articulates with the ramus towards its 
distal end and extends outwards. 
(5) The lower jaws of the Histriobdellid^e are 
apparently not represented at all in the mastax of the 
Rotifer, unless we are to look on them as corresponding to 
greatly developed posterior parts of the manubria. 
(6) The entire apparatus, it is important to note, is situated, 
not in the interior of the enteric canal as in the Rotifer, but 
in a blind pouch (pharynx) which lies on the ventral side of 
the oesophagus and opens on the exterior through the mouth. 
In Paraseison alone among the Rot if era does the mastax 
occupy a corresponding position. 
I am able to supplement my earlier account of the jaws of 
St ratio dr ill! s by certain additional particulars regarding 
the rami of the upper jaw and to give more detailed figures 
of them (figs. 26, 27). Each ramus consists of four sets 
(ramules) of movably articulated chitinous pieces, each 
ramule ending in a tooth. Of these four teeth only the 
outer two have the curry-comb-like character to which I 
previously directed attention (6, p. 307). The other two are 
