are ascribed the species which are transmitted through intermediary hosts 

 through which a specific part of the life cycle of the parasite passes. How- 

 ever, this division, although it has a positive significance from our point of 

 view because it underlies the difference in the methods of infection, is 

 clearly insufficient, w^ithout even mentioning the fact that the terms them- 

 selves are extremely unsuccessful. V. A. Dogiel proposes to differentiate 

 two means of penetration of parasites into the host organism and, in this 

 connection, to divide the parasites of the two groups --with exogenous or 

 endogeneous methods of penetration. However, it seems to us that it is 

 more important to turn attention to other peculiarities of the means of in- 

 fecting the host; namely, on the element of activity of a given process. In 

 connection with this, we suppose that the most important biologically is the 

 division of the parasites into two different groups on the basis of their mode 

 of infection of the host, namely: (1) infecting the host by an active larva 

 settling independently on the body of the host or penetrating into it; (2) in- 

 fecting the host passively by means of the host itself (namely by way of the 

 food through the mouth). 



This division bears a different character than the two indicated 

 above but does not represent anything particularly new because it has often 

 been used in parasitological literature (see Pavlovsky, 1946). 



To the first group, that is, actively infecting the host, pertains 

 the huge majority of ectoparasites, and particularly the basic mass of 

 monogenetic trematodes. A number of endoparasites are also related here. 

 The second group contains the basic mass of endoparasites and also a small 

 number of ectoparasites (see Dogiel 1947, pages 63-71). In certain cases 

 the infection takes place, so to speak, by a nnixed way- -in the beginning the 

 parasite actively seeks the host and then the latter swallows it during 

 breathing; undoubtedly this method of infection would be more correctly 

 attributed to the first category. Often, among forms which have alternation 

 of generations, the active method of infection alternates with the passive. 

 Thus, the miracidium of many trennatodes penetrates into the first inter- 

 mediary host actively, whereas the cercaria penetrates into the second 

 passively during the consumption by it of the first; adolescaria penetrate 

 into the final host just as passively. Without entering into the discussion 

 of the details of common normalities of the process of infection, it is 

 indispensable to indicate that in our opinion the two named types of infection 

 have a very important significance for the development of specificity of 

 parasites. 



Let us pause briefly on the peculiarities of active infection. 

 The first condition for it is the presence of an actively moving larva pos- 

 sessing adaptations for recognition of the subject which must be "attacked" 

 in order to infect it. The second conditions are the morphobiological p. 290 



peculiarities of the given larva which allow it to settle, to attach itself ona 



333 



