The hatching phenomena of Clonorchis ova.

Ova of Clonorchis have a high specific gravity, as they sink in concentrated saline solution within one-half hour, and in pure glycerine (Sp. gr. 1.26) in 48 hours. The shells show markings of an arabesque pattern, best brought out by staining with weak potassium permanganate of toluidine blue. They contain fully developed embryos at the time of discharge from the worm. In spite of these facts, under experimental conditions which may also hold true in nature, they would not hatch out but would degenerate if left undisturbed. Various external factors may operate upon these eggs either singly or in conjunction. The more important of these are as follows:

(a) Mechanical, e. g., pressure of needles in teasing out the eggs; the pressure of cover-glass, or the running in of H₂O under the latter and subsequent streaming with filter-paper. A heavy pressure short of crushing the embryo, on the cover-glass, will cause the lid to give way and the embryo to be thrown out passively. A light pressure, e. g., touching with the point of a teasing needle, on the other hand, will waken the dormant larva and set its cilia in motion, with the body alternately contracting and extending. Rolling, thrusting and corkscrew movements have been observed, but round-about-turns, as seen in the case of Schistosoma larvæ, have never been noticed. The perfectly tight fitting nature of the hard shell would not admit of this. This attempt is often attended with success, but sometimes with failure. In the former case, one side of the operculum would be seen to give way by a forward thrust, aided no doubt by increasing iaternal pressure, through the opening of which the larva would launch forth, spine foremost, like a torpedo out of a man-of-war.