440 REPORT—1905. 
protozoal diseases to domesticated animals has been fully demonstrated. We 
reserve a detailed treatment of the subject for a future paper. 
A tick is a headless creature whose brain lies within its body. The so-called 
‘head’ is really made up of mouth parts and appendages which protrude from the 
body anteriorly, the whole being termed the rostrum. The rostrwm consists of a 
basal ‘ring’ of thick chitin, which articulates posteriorly with the ‘ dorsal shield,’ 
and is continuous laterally and ventrally with the softer and thinner integument of 
the front of the body. The ring bears two palps, two mandibles, and a hypostome 
(representing the fused maxillz of other Arachnida). 
The palps are tactile organs, are articulated antero-laterally upon the ring, and 
do not serve as organs for penetrating the skin; in fact, when the tick is fixed upon 
the skin of the host the palps are turned outwards at right angles to the remaining 
mouth parts. The boring organs are the mandibles, which lie side by side dorsally, 
and the hypostome situated ventrally to the preceding, 
The mandibles, which are homologous with the chelicere of Arachnida, consist 
of long tubular first joints; the latter are enveloped in sheaths and pass out from 
the body tbrough the ring, the chitin of which is continuous with a thick outer 
mandibular sheath which folds backwards distally. This outer sheath is provided 
with minute, closely ranged, recurved teeth which give the surface a shagreened 
appearance dorsally and laterally. The shagreened sheath may be compared to a 
pair of trousers, the chitin at the ‘waist’ being continuous with the ring and then 
dividing to form the two legs, only that the legs cohere along the inner seam, and 
at the end of the trousers leg the chitin again folds inward and backward, ulti- 
mately fusing with the inner sheath, which, so to speak, represents the under- 
clothes. These sheaths obviously permit of considerable antero-posterior movement 
of the tubular joint of the mandible. The latter ends distally in a second, short- 
toothed joint presenting a very minute and delicate structure which would 
require a too lengthy description for this occasion. It consists of a first article, 
formed basally, like a knuckle, and articulating upon the extremity of the tubular 
first joint. This article contains a cavity communicating backwardly with the 
‘tube’ and outwardly through a pore in the end of the toothed process, in which it 
terminates distally. A second article is articulated upon the outer, and a third 
upon the dorsal surface of the first article; and these, which are also provided 
with sharp teeth, contain cavities which are continuous with that of the first 
article. Two sets of muscles which run within the tube move this tooth-complex 
from side to side; a more powerful external set joins on to a stout tendon running 
to the outer protuberance of the ‘knuckle’; a much weaker set pulls on a more 
delicate tendon running into the internal protuberance. As was shown by lan- 
tern-slides, the sharp recurved teeth, especially of the second article, are turned 
outward, consequently these serve as organs for penetrating the skin, and, wher 
everted, literally anchor the parasite. It is obvious why the muscles which evert 
the second article should be more powerful than the internal. Apart from this, 
the mandible as a whole is retracted by powerful muscles running from the dorsal 
shield of the tick to the inner end of the tube and its sheath. The firm shagreened 
double-barrelled sheath gives an additional hold and greater rigidity. 
The hypostome protrudes forwards like the under-bill of a duck ; posteriorly it is 
continuous with the thick, chitinous ring. Its ventral surface is covered with 
stout recurved teeth, and on its dorsal surface is a median V-shaped groove. The 
hypostome is in close contact with the mandibles, and is dragged into the wound 
formed by the latter. Once it has entered it secures a firm hold by means of its 
recurved teeth, The hypostome is thickened and expanded at its base, where its 
external surface fuses with the basal ring, and its internal (dorsal) surface gives 
rise to the attachments of the upper end of the alimentary canal. 
The buccal cavity, as we term the commencement of the alimentary canal, is a 
small shallow space enclosed by chitinous walls. A thickening of the fused 
sheaths of the mandibles, and a backward prolongation from the base of the 
hypostome, form respectively the roof and floor of this space, which is completed 
laterally by thick masses of chitin joining these two parts. A groove, continuous 
with that on the dorsal surface of the hypostome, runs along the floor of this 
