580 DESCRIPTION OF THE SUBGENUS ECHINOCOCCIFER. 



such a manner that the original Echinococcus is changed into a system 

 of cysts enclosed one within another. These resemble vesicles of 

 Volvox, to which this parasite has indeed often been compared, and 

 represent so many generations enclosed one within the other, and 

 capable of producing tape- worm heads in the same manner as the 

 mother-bladder. In other cases, as we shall afterwards see, the 

 process of proliferation yields buds, which make their way outwards, 

 and are developed beside, the mother-bladder. 



The Tcenice, which are developed from the Echinococcus-heads in 

 the intestine of the dog and related animals, are extremely small, and 

 have but few joints ; so that in this respect there is a striking differ- 

 ence between them and the cystic tape-worms of the previous group. 

 The hooks are proportionate in size to the head, but are otherwise 

 formed like those of the cystic tape-worms. 



Whether there are several species of Echinococcus is a question that 

 has been much discussed by investigators. The early helminthologists 

 (with Rudolphi at their head) generally accepted two species, 

 Echinococcus hominis and E. veterinorum, which differed principally 

 in that the former contained numerous daughter and granddaughter 

 bladders, while the latter consisted usually of a simple bladder. It 

 has long since been proved, however, that the composite form, Echino- 

 coccus hominis, is also occasionally found in the ox and other mammals 

 (such as the horse, pig, and kangaroo) ; and, vice versa, that the human 

 Echinococcus not unfrequently possesses the simple structure of the 

 E. veterinorum. Sometimes one even finds two forms of Echinococcus 

 side by side in the same individual. 1 It has also been repeatedly 

 noted that it is difficult to differentiate the two forms sharply from 

 each other, since the number of the daughter-bladders varies consider- 

 ably, being sometimes very large, and at other times limited to a few, so 

 that the compound Echinococcus gradually changes into the simple one. 2 



On these grounds many distinguished helminthologists (such as 

 my uncle F. S. Leuckart, Creplin, v. Siebold, and Diesing) have denied 

 that there is any warrant for the separation of these two species, and 

 have explained the indicated differences as mere individual varieties. 

 But at a later period Klichenmeister 3 has again spoken in favour of 

 the old idea, except that he changes the specific names Echinococcus 



1 This sometimes happens in the pig, as is shown by Dupuy's case, quoted by Davaine 

 (Journ. mM. de Sedittot, t. xcii., p. 63, 1823). In the different muscles, in the lungs, 

 liver, and kidney, Echinococci were found, some of which were solitary, whilst others 

 enclosed daughter-bladders within them. 



2 Eschricht mentions a case (of Krabbe's) in which an Echinococcus of the size of a 

 child's head only contained two small free-swimming bladders. A counterpart is furnished 

 by those cases in which the number of the endogenous bladders might be estimated at 

 several thousands. 



3 "Parasiten," first edition, p. 139. 



