H^EMATOZOA. 49 



mentioned, no true parasite, but the mature state of a heteromorphous 

 species, the so-called Anguilhda intestinalis. The young are born in 

 the intestine of the host, and attain maturity (like Ehabditis} only 

 after abandoning the latter ; they live in the same way as Rliabditis 

 terricola (Fig. 30), and then give rise to a new generation. 1 



It appears, therefore, that the following generalisation may be safely 

 made : There are no intestinal worms, at least among the typical and 

 constant parasites, whose embryos come to maturity near the parent ; 

 or, in other words, there are none which pass their whole life-cycle in 

 one locality* 



If we now turn to the embryos arising from these so-called worm- 

 nests, it seems clear that they by no means reach further develop- 

 ment in the body of their host, but after a longer or shorter period 

 abandon it for a free external life. All the little that we know by 

 direct experiment agrees with this. Ecker discovered in the body- 

 cavity and blood-vessels of his rook numerous small Filaria-like 

 Nematodes, which he considered to be the embryos of Filaria attenu- 

 ata, 3 and he found them in a later stage as small worms measuring about 

 a line, encysted in the mesentery and other places. Vogt has made 

 similar observations ; 4 he discovered in the body-cavity of a frog two 

 large Filarice, more than an inch long, containing numerous embryos ; 

 the latter he also observed circulating in the blood. Lewis has also 

 shown that numerous Hsematozoa are found in dogs afflicted by Filo.ria 

 sanguinolenta, and the same thing was observed by Gruby and 

 Delafond; 5 and later by Leidy and Walch, 6 in cases where Filaria 

 immitis was present in the right heart of the same animal. In the 

 case last mentioned the embryos have no difficulty in getting into 

 the blood, since they inhabit from the first an organ which they 

 could reach otherwise only by means of an active migration. 



1 Leuckart, " Lebensgeschichte der sog. Anguillula stercoralis, u. deren Beziehung zu 

 d. sog. A. intestinalis," Bericht math. phys. 01. Ic. Sacks. Gesettsch. d. Wiss., p. 85, 

 1882. 



2 I use the term "intestinal worms" instead of "Entozoa" advisedly, since among 

 Gregarine parasites there are many which regularly reach maturity near their parents. 

 In other cases, where the germs grow to embryos at large, there is a regular migration, as 

 in intestinal worms, to and from the body of their host. 



3 Heematozoa, arising from Filaria attenuata, are very commonly met with at Leipzig. 

 Of 38 crows which Kahane examined for this parasite at my suggestion, 28 i.e. 80 

 per cent. contained it, and sometimes in such abundance that the smallest drop 

 of blood contained quantities of them. By examining a certain amount of blood, the 

 weight of which had been previously ascertained, it was found that 1 mgrm. of blood con- 

 tained 601 embryos, which means that the whole of the blood, reckoning it at y^th of the 

 whole 360 gr. net weight, would contain about 18,000,000. 



4 Archivf. Anat. und Physiol, p. 189, 1842. 



5 Comptcs Rendus, t. xlvl, p. 1217, 1858. 



6 Monthly Micr. Journ., p. 157, 1873. 



D 



