L. E. Robinson and J. Davidson 
405 
the shell is probably secreted by the epithelial lining of the oviduct. 
All who have written on the subject of the genitalia of the ticks are 
curiously reticent on this point, and it appears to us to be by no means 
unimportant, in view of the fact that pathogenic protozoa— e.g. Piro- 
plasma bigeminum —are transmitted from the female tick, via the egg, 
to the larva, which is thus infective from the time of hatching. 
The Oviducts. 
The oviducts ( d. ov.) consist of a pair of relatively thick-walled tubes 
which take their origin from the lateral extremities of the ovary, from 
which they run forwards, following a convoluted course, as far as the 
anterior extremity of the uterus; at this point they suddenly turn 
inwards and backwards and run along the lateral margins of the uterus, 
which they enter at its respective posterior angles. From the point 
where the course of the oviducts is reflected to their union with the 
uterus, their diameter is considerably enlarged. 
The wall of the oviduct is formed of three layers,—an inner epithelial 
layer of very elongated columnar cells, with small pale nuclei situated 
near their bases—a middle layer of muscular fibres, disposed in a circular 
direction, but upon the external surface of which a number of separated 
longitudinal muscle bands are disposed—and an outer layer of flattened 
epithelial cells. The free margin of the columnar cells of the lining 
epithelium usually presents a frayed'and ragged appearance, and the 
cells encroach so far into the interior of the tube as to almost occlude 
its lumen. The upper and thinner portion of the oviduct differs some¬ 
what from the lower portion, in the fact that the muscular layer is not 
so strongly developed, while the epithelial lining is almost suppressed 
on one side of the duct, and as the remaining epithelial cells extend 
across the duct for some distance beyond its centre, the lumen is 
excentric. 
The lower and thicker portion of the oviduct ultimately becomes 
distended with spermatozoa and the histological details of its walls are 
to a great extent destroyed. 
The Uterus. 
The uterus ( ut .) is a large median unpaired sac of triangular form 
which is situated in the middle of the body, between the stomach and 
the ventral body wall. The posterior angles are somewhat drawn out 
in the form of cornuate extensions, into the extremities of which the 
oviducts open. 
