A. D. Peacock 113 
do not show this. The tip consists of two minute mandibular dilatations 
toothed on the outer edges. 
The ventral element commences as two rami, ventral and internal to those 
of the dorsal elements. They are straight and have the widest span of all the 
paired rami. They run forward in the floor of the sac, then converge and grow 
wider inwards till they fuse as a groove which fits exactly into the sac floor 
groove. So exact is the fit that for a long time I was inclined to think that 
the ventral element was a u split away ? ’ from a sac groove which, as figured 
by Harrison, had posterior rami. Further investigation, however, shows that 
the sac floor groove ends bluntly and that the posterior rami belong to the 
ventral element of the ventral stabber. The tip is similar to that of the dorsal 
element, only the mandibular dilatations are larger and outermost. 
At first the two elements of the ventral stabber fuse along their margins 
only but ultimately they fuse along their length. The anterior two-thirds of 
the ventral stabber is therefore composed of two elements, dorsal and ventral, 
each element having a separate origin posteriorly. Cross-sections of the 
stabber anteriorly show that fusion is not complete as two minute cracks 
are visible in the chitin, each one beneath what is left of the lateral grooves. 
In dissections, too, the elements may readily be split from one another. 
The space between the upper and lower portions of the stabber, before 
their fusion, is occupied by tissue which commences posteriorly, as connective 
tissue, similar to the general connective tissue of the head, and is packed 
between the posterior muscles of the stabber and the floor of the sac. Beneath 
the region where the dorsal groove begins, it becomes a distinctly character¬ 
istic tissue, consisting largely of blue-staining cells with very dark-staining 
nuclei. Further forward the tissue stains red and appears to be similar to 
that of the dorsal stabber. 
The function of these stabber tissues is probably twofold in (1) bending 
or turning of the stabbers while in action so as to assist boring into the 
skin of the host, (2) regenerating, in the larval stages, the stabbers, before 
ecdysis. 
Stabber Muscles (PI. VI, fig. 1, Text-figs. Ill—V). These consist of one 
pair of protractors which operate both the stabbers and the sac, two pairs of 
retractors of the sac, one pair of retractors of the dorsal stabber and one pair 
of retractors of the ventral stabber. 
(1) Protractors—one pair (s.pr.). These are the “musculi digastrici of 
Pawlowsky who‘does not describe their nature and function exactly. Each 
muscle has two origins on the sac, one dorsal and the other ventral. The dorsal 
origin is situated slightly to the side and above the orifice of Pawlowsky’s 
gland. The ventral origin is anterior to the dorsal and is situated nearly as 
far forward as the anterior part of the sac floor groove and inside the lateral 
floor groove. The two branches run backwards and gradually converge to 
unite on the side of the sac about half way along its length (PI. VI, fig. 1, 
Text-figs. IV, V). The muscle then runs along the # wall and gradually rises 
Parasitology xi 8 
