348 Dr Eschricht's hiquiries concerning 



semblance to the mother. In the intestines of these young 

 ones, there is a certain part already existing dm'ing their 

 stay in the ova within their parent, which is changed in the 

 most extraordinary manner into another intestinal worm, ap- 

 pently belonging to quite a different genus, viz. that of the 

 Distoma. Thus in the bird, the worm has a young one, in 

 which a third is developed, but the young one is soon after its 

 birth destroyed by the youngest, which thus becomes free. 

 This very singular enclosing of one generation within another 

 has been interpreted by some authors as a multiplied spon- 

 taneous development, or as a series of abortive attempts of the 

 formative power. The constancy, however, of the fact forces 

 us rather to consider it as a series of metamorphoses ; and the 

 rather, as more than a single worm is never included in each 

 individual, and this one invariably. As the young in the last 

 observed stage are still as different from the parent as in the 

 former ones, it may be a question whether this metamorphosis 

 is the last. 



Again, the well-known observations of Nitzsch, Bojanus, 

 Baer, and more lately of Siebold (1. c), on the Cercarice, and 

 the curious living sacs in which they are developed ; those of 

 Bojanus on the Distoma duplicatum and Bucephalus polymor- 

 j)hus, and those of Cams on the Leucochloridium paradoxum, 

 all appear to us, in the present state of the science, in the light 

 of most extraordinary facts, chiefly because they are like the 

 first -discovered plants of a terra incognita, which promises the 

 richest harvest to future inquirers. 



Sect. 4. The manner of Prop>agation of the Entozoa supposed 

 to be very complicated. — It being once established that intesti- 

 nal worms regularly change their forms and abodes, we cannot 

 much wonder that their mode of introduction into the body 

 can never be divined. If we turn our attention to the history 

 of those creatures whose change of abode and shape is more 

 familiar, we may demand. Was there one case among them in 

 which that history could have been ascertained in any other 

 way than by the most laborious research, or which, if conjec- 

 tured, would not have been considered altogether fabulous .'' 

 Thus is it with the development of the Ichnewnons in the inte- 

 rior of other insects, and with the various methods in which the 

 mother-ichneumon introduces the ova into these insects I The 



