ANIMAL PAEASITES. 51 



instinct. But when Leuckart goes on " where the embryo can- 

 not go further, there it remains seated," I only adopt this view 

 if we add "for the present, for an indeterminate (probably 

 very short) time." Here, indeed, I must for the present 

 differ from Leuckart, for various reasons. I suppose that as 

 soon as the embryo becomes fixed [in the capillaries], it, as it 

 were, awakens again, and again sets about migrating actively 

 through the walls of the capillaries, or if it remains stuck in 

 the capillaries, it rather dies, or by thrombus-formation and 

 thrombous diseases thereby produced, very rapidly causes the 

 death of its host. Every one will admit that the extraordinarily 

 speedy death of the animals experimented on may be best 

 explained by the supposition that death is produced by the 

 tearing away of blood-coagulum (Thrombose). The immediate 

 active exit of the little brood, appears to me to be supported by 

 the circumstance that the desire of active migration in these 

 little creatures, as is shown by the formation of passages upon the 

 liver and in the brain, still exists at a period when they have 

 already become developed into vesicles which may be very clearly 

 perceived with the naked eye, and is proved by the fact that even 

 ten or eleven davs after administration, such visible Ccenurus- 

 vesicles are found free upon the convolutions of the brain. From 

 the considerable extensibility usually possessed by the walls of 

 vessels, we may well suppose that with this bulk these walls would 

 not be burst, but that a greater dilatation of the vesicle would 

 be necessary for this purpose. It is also remarkable that we 

 do not usually meet with effusion of blood so much as mere 

 plastic exudations. All this is most easily explained by the 

 supposition that the smallest brood, when scarcely or incon- 

 siderably dilated, emigrates at once directly from the blood- 

 vessels. Moreover, Leuckart has not succeeded by his experi- 

 ments in injection, in proving that the Cystic, pisiformes remained 

 fixed in the interior of the finest ramifications of the vena 

 porta. As he says himself, the mass of the injection only 

 reached the position of the Cysticerci after the rupture of the 

 capillaries. The question can only be finally settled by the re- 

 discovery of the six small embryonal hooklets upon the Cysti- 

 cercus. If Leuckart's statement — that these six embryonal hook- 

 lets are discoverable upon Cysticerci pisiformes seated free in the 

 liver — be confirmed, these hooklets, by which " its destiny to 

 wander is written upon the forehead of the embryo," furnish 



