^119. 



THE HELMINTHE3. 



131 



nic cells present the same successive phases as in the Cestodes and Trema- 

 todes, without the appropriated vitellus undergoing any segmentation ; or, 

 the whole vitellus after a complete segmentation, is changed into an em- 

 bryo/'' 



In both cases, the embryo has the parent's form. A muscular oesopha- 

 gus and straight intestine appear in its body in the midst of the refuse 

 vitelline granules; and thus the young animal attains its perfect state by 

 simple increase and by the development of its genital organs, but without 

 any metamorphosis/-' 



From the few observations hitherto made upon the development of the 

 Gordiacei, it appears that the embryos exactly resemble the parents/''' 



1 KollikeT was the first to call the attention to 

 these two types of development with the Nema- 

 todes {Muller's Arch. 1843, p. 68, Taf. VI. VII.). 

 With Ascaris dentata, Oxyuris ambigua, and 

 Cucullanus elesans, free embryonic cells are 

 formed in the vitellus without its fissuration. But 

 there is a complete segmentation with Ascaris 

 nigrovenosa, acuminata, succisa, osculata, 

 labiata, and brevicaudata, Strongylus auricu- 

 laris, dentatus, Filaria injlexo-caudata, rigida, 

 and Sphaerularia bombi. After I had already 

 noticed this vitelline segmentation with the Ne- 

 matodes {Burdacli's Phys. loc. cit. p. 211), which 

 Bagge (Dissert, loc. cit.) described very fully, 

 KoUiker (loc. cit.) attempted to reconcile it with 

 the cell-theory, by regarding the cells which 

 appear in the segmented, vitelline globules, as the 

 embryonic cells, and in the multiplication of 

 which by segmentation, the enveloping viteUus 

 participates. 



2 It appears that, as with the Trematodes, so in 

 the Nematodes, a migration of the young precedes 

 their complete development. 



In the tissues of the most different insects and 

 vertebrates, there are found small Nematodes 

 without genital organs, and contained in a cyst. 

 They could not get there except by a migration, 

 and they cannot attain the full development of 



their genital organs or their bodies in general, 

 except through a transplantation upon other ani- 

 mals ; exactly as occurs with the trematodal larvae. 

 (See the observations of Creplin and myself upon 

 the sexless Trematodes, in WiegrnaniVs Arch. 

 1838, I. p. 302,«373.) 



The Trichina spiralis of ma,n is undoubtedly an 

 encysted and imperfect form of one of the Nema- 

 todes, and in which one may seek in vain for gen- 

 ital organs. Some of these Nematodes appear to 

 increase in their cysts without their genital organs 

 being developed in the same proportion. Thus, the 

 Filaria piscium are sometimes found very large, 

 while their genital organs are very little developed ; 

 and these last do not probably attain their perfect 

 state, until, as with Bothriocephalus solidus, 

 these worms have passed into other animals. For 

 the same reason, I agree with Steenstrup (loc. cit. 

 p. 113), who doubts that the Filaria piscium 

 become, as Miescher has affirmed (loc. cit. p. 26), 

 a globular capsule out of which there afterward 

 appears an animal at first resembling a Trema- 

 tode, but which finally becomes a Tetrarhyn- 

 chus.'' 



3 See Dujardin (Ann. d. Sc. Nat. XVni. loc. 

 cit. PI. VI. fig. 15, 16) upon Mermis nigrescens, 

 researches which I have been able thoroughly to 

 confirm.! 



kind of nurse of a Distomum, containing peculiar 

 germ-bodies wliich are developed into Disiomum. 

 But the most important result obtained is that all 

 Distomum are not developed by means of a cer- 

 carian, larval stage, — the economy of some making 

 it seemingly requisite that the developmental pro- 

 cess should be more direct. — Ed. 



* [ § 119, note 2.] In regard to Trichina spi- 

 ralis, the various researches upon its structure, 

 made in England and America, would show that it 

 is a true animal having genital organs. The fol- 

 lowing are some of the references upon this sub- 

 ject : Owen, London Med. Gaz. April and Decem- 

 ber, 1835, or Transact. Zool. Soc. London, IV., or 

 Cyclop. Anat. and Phys. Art. Entozoa; Wood, 

 London Med. Gaz. May, 1835 ; Farre, Ibid. De- 

 cember, 1835 ; Harrison, Report of the Brit. 

 Assoc, for the Advancem. of Sc. 1835 ; Knox, Edinb. 

 Med. and Surg. Jour. 1836, XLVI. p. 86 ; Hodg- 



kin, Lect. on Morbid Anat. of Serous and Mucous 

 Membranes, I. p. 212 ; Cjirling, London Med. 

 Gaz. February, 1836 ; Bowditch, Boston Med. and 

 Surg. Jour. April, 1842 ; Luschka, Siebold and 

 Kolliker's Zeitsch. III. 1851, p. 69, Taf. III., and 

 Gairdner, Edinb. Monthly Joui'. of Sc. May, 

 1853. The subject is one that deserves especial 

 attention from Ilelminthologists. — Ed. 



t [§ 119, note 3.] Grube {JViegmann's Arch, 

 fiir Naturgesch. 1849, p. 358) and Leidy (Proc. 

 Acad. Sc. Philad. V. 1850, p. 98) have observed 

 the development of Gordius. It corresponds 

 pretty closely with that of Ascaris as described by 

 Bagge ; but the embryo on escaping from the egg 

 is annulose and tentaculated, and differs much 

 from the adult form. Nothing is known of the 

 history of the animal between these two conditiona. 

 — Ed. 



