822 Proceedings of Royal Society of Edinburgh. [sess. 
in length and 32 to 43 in breadth. Although the fully-developed 
American ankylostoma is smaller than that of man, the ovum of 
the parasite is somewhat larger. The ova of the human 
ankylostoma have a well-defined external covering. Occasionally 
a small space is left between the contents of the ovum and the 
capsule. Usually the protoplasm is observed to he undergoing 
segmentation, when four or more blastomeres may be noticed. 
When the segmentation is complete, the ovum is said to have 
reached the morula stage, but this does not last long, for shortly 
afterwards the developing larva can be seen rolled up on itself, and 
sooner or later the capsule ruptures and the organism escapes. 
On examining the stools of infected miners a distinction has 
to be made between the ova of ankylostoma and those of other 
parasites, for miners who harbour the ankylostoma are often 
unconsciously the hosts of other intestinal parasites as well. 
The ova of Oxyuris are haricot-bean-shaped, while those of 
Tricocephalus dispar are smaller than those of the ankylostoma, 
are lemon-shaped, and often exhibit an iron-grey colour. The 
ova of Tcenia solium are round and have a thicker capsule ; those 
of Bothricephalus latus are still larger, and have a thin capsule, 
which is completely occupied by the contents. The ova of Ascaris 
lumbricoides are smaller and are rounder than those of the 
ankylostoma ; they are mulberry-looking and have a thicker 
capsule, which often exhibits a double contour. 
The ova of the Ankylostoma duodenale do not undergo segmenta- 
tion in water, and yet complete deprivation of water kills them. 
They develop, however, in soft liquid material. They require, it is 
generally stated, a temperature from 20° to 30° C., or from 68° F. to 
86° F. Coal mines with a temperature below 60° F. would therefore 
not be very favourable to the development of the ova. Tenholt 
found in Westphalia, when the temperature of the mines was 
reduced by freer ventilation, that the disease ceased to spread in 
the pits ; but Lambinet and others have demonstrated that the ova 
can become transformed into larvse in coal mines at even lower 
temperatures than 57° F., although at this temperature the larvse 
come into existence very tardily, and, as a rule, are short-lived. 
Higher temperatures than 98° F. destroy the ova ; the ova do not 
hear very well sudden variations of temperature. The ova must 
