which are developed in cold-blooded animals ; but, in 

 those which are found in the warm-blooded animals, 

 a passive as well as an active migration takes place. 

 The embryos bore through the tissues into the blood- 

 vessels, and are then carried along by the circulation, 

 until they bring up in some of the smaller vessels, 

 which they then leave as they entered. Leuckart 

 four times found free embryos in the blood of the 

 main branch of the vena porta at its entrance into 

 the liver; and Kuchenmeister also, in speaking of 

 this subject, remarks, that he is " convinced that the 

 brood is introduced into the circulation of the blood 

 by the active penetration of the tissues, and then a 

 passive migration with the blood is commenced." 

 The supposition, entertained by Kuchenmeister and 

 Haubner, that these embryos penetrate the abdomi- 

 nal cavity and the organs therein contained through 

 the ductus choledochus, has not been supported by 

 Leuckart; and there is reason to believe it is un- 

 founded. 



To sum up the manner of the migration of these 

 embryos : 



1. A portion of the six-hooked brood in all species 

 of Cestoidea (whether in cold or warm-blooded ani- 

 mals) may reach their dwelling-place directly, and by 

 active migration. 



2. Another portion, after a longer or shorter mi- 

 gration, reaches the vascular system of the new host 

 (the blood-vessels, and perhaps also the lymphatic 

 system, as, according to Virchow, is the case with the 

 Echinococci) ; is subjected to a passive migration hero 



