40 



OVUM. 



Additional Remarks. * Since the foregoing 

 observations on alternate generation were 

 printed in* August, 1852, the knowledge of 

 these peculiar phenomena and of the whole 

 forms of reproduction in various classes of 

 animals has been considerably augmented by 

 several important contributions. A short 

 reference to some of these researches seems 

 necessary in this place, in order to complete 

 our notice of the phenomena referred to. 



The statements of Stein, referred to at 

 p. 7 of this article, as to the encysted condi- 

 tion of the Vorticellae previous to their under- 

 going multiplication, having been called in 

 question by Ehrenberg*, the subject has been 

 farther investigated by F. Cohn, with the re- 

 sult both of a full confirmation of Stein's state- 

 ments, and of its being ascertained that a 

 considerable number of other infusoria are 

 subject to a similar change ; among which he 

 mentions species belonging to the genera 

 Euglena, Prorodon, Chilodon, Notophyra, 

 Trachelius, Trachelocera.and Stentor.-j- Stein 

 holds it to be fully established that the nucleus 

 of the Vorticella is its true reproductive or- 

 gan. From this nucleus a progeny is formed 

 in two modes, in both of which the parent 

 animal becomes encysted. In one mode the 

 encysted Vorticella is converted into an Aci- 

 neta-form by the prolongation of narrow con- 

 tractile processes of its substance from the 

 external surface, and from the nucleus of this 

 Acineta-like animal successive single ones are 

 produced by gemmation. In the other form, the 

 nucleus of the encysted Vorticella undergoing 

 subdivision, becomes converted into the 

 germs or spores of numerous new Vorticellae. 

 This process is probably in these Protozoa 

 the equivalent of a sexual production of ova ; 

 and appears to correspond nearly with that 

 which takes place in the production of the 

 Navicella-like progeny from Gregarinae, with 

 this difference, that in the latter case two 

 Gregarinae are united or fused together into a 

 sphere previous to the production of the new 

 progeny or spores, 



The view of Leydig, therefore :, that the 

 parasitic infusoria named Gregarinae are only 

 an imperfect or metamorphosed condition of 

 a Filaria, does not appear to be confirmed. 



In reference to the Entozoa, recent experi- 

 ments have" furnished ample confirmation of 

 the views now adopted by almost all physiolo- 

 gists, that these animals are the product of a 

 true sexual generation, and that their ova, or 

 embryoes, or larva?, are introduced from with- 

 out into the bodies of those animals which 

 they parasitically inhabit ; while at the same 

 time the knowledge of their migrations and 

 remarkable transformations becomes more 

 and more precise from additional and renewed 

 investigation of their different forms. 



Herbst, who had previously failed in some 

 experiments to cause the transmission of the 



* Bericht of Berlin Acad. for 1851. 



} Zeitsch. fiir Wissen. Zool., vol. iv. p. 253. 



j On. Psorospennia and Gregarinre, in Midler's 

 Archiv. for 1851, translated in Quart. Journ. of 

 Micro. Science. 



Trichina? of the muscles by implantation in 

 wounds of animals, at last succeeded in 

 1850-51 in causing the muscles of several 

 young dogs to be infected with these parasites 

 by giving them to eat the flesh of a badger which 

 had lived with him for some time in confine- 

 ment, and in which the Trichinae existed in great 

 quantity.* About the same time Kuchen- 

 meister found that by causing young dogs to 

 swallow along with their food a quantity of the 

 Cysticercus pisiformis (of the hare and rabbit), 

 the intestines of these animals were in a few 

 weeks invariably occupied by a Taenia (T. ser- 

 rata). Von Siebold, who, as has before been 

 remarked, was the first to advance the opinion 

 (in 1844), that the Cysticercus fasciolaris in- 

 habiting the liver of the rat and mouse is 

 only the early condition of the Tjenia crassi- 

 colis of the intestine of the cat, has with the 

 assistance of Lewald performed a series of 

 experiments of a nature similar to those of 

 Kuchenmeister, which have established be- 

 yond doubt that various^ kinds of Cysticerci, 

 and also the Caenurus of the sheep's brain, 

 and the Echinococcus veterinorum, are always 

 converted into Tasniae or Cestoid Worms within 

 a short time after they have been transferred, 

 as by feeding, into the alimentary canal of 

 suitable animals. These experiments have 

 also afforded to V. Siebold the means of ob- 

 serving in a most interesting manner the pro- 

 cess of development and gradual conversion 

 of the cystic into the cestoid entozoon.-f- 



Since the publication of V. Siebold's ex- 

 periments, farther researches on the same 

 subject have been laid before the Academy of 

 Sciences of Paris by Van Beneden and by 

 Kuchenmeister, in Memoirs presented by 

 them in competition for the grand prize of- 

 fered by the Academy in 1853 for the scien- 

 tific investigation of the Development and 

 Transmission of Intestinal Worms. J 



The observations and experiments com- 

 municated by Van Beneden in this prize essay, 

 and those contained in his highly interesting 

 Memoir on the Cestoid Entozoa, published 

 in the Memoires de 1' Academic Royale de 

 Belgique for 1850, have also established in 

 the most satisfactory manner the relation be- 

 tween the encysted or scolex condition and 

 the cestoid form of the Tetrarhynchi ; facts 

 which have also been in part confirmed by R. 

 Wagner. Van Beneden has observed the 

 first development of the ova of the Tasnia 

 dispar of the liana temporaria || into the small 

 embryo provided with its three pairs of boring 

 booklets, and has watched with care the ac- 

 tive motions of these instruments, by which 



* Ann. des Sc. Nat., 1852, torn. xvii. p. 63., and 

 in Quart. Journ. of Micro. Science, No. 3. p. 209. 



f Zeitsch. fiir Wissen. Zool., vol. iv. pp. 400. 409. 

 See particularly Plate xvi. A. Also in Annal. 

 des Sciences Nat, 1852, and L'Institut., No. 974. 



J See the Report of the Commissioners, by Qua- 

 tretages, in Comptes Eendus for Jan. 30th, 1854. 

 p. 16b. 



See extract of a letter in Ann. des Sc. Nat. for 

 1853, vol. xix. p. 179. 



|| Comptes Rendus, 1853, p. 788., and in Aunals 

 of Nat. Hist., vol. xiii. p. 157. 



