NEMATODA 241 



tinctly oval shape, the true yolk-membrane and the external 

 chorional envelope now becoming more and more differentiated, 

 until the latter acquires a regularly tuberculated surface. Co- 

 ordinating with these changes the granular yolk is seen trans- 

 forming itself into a single large embryonal cell ; after a time 

 this cell divides and subdivides by the ordinary process of 

 yolk-segmentation, until it is finally resolved into the condition 

 of a short, stout, vermiform embryo. The egg having assumed 

 its definitive oval shape, the intrachorional embryo remains 

 coiled within the shell, and does not make its escape until the 

 egg has passed from the body of the parent worm. 



Into the question of the mode of formation of the ovarian 

 ova, and also into that of the development of the spermatozoa, 

 I do not enter. However unwillingly, I must, in this matter, 

 be contented to refer to Professor Allen Thomson's classical 

 article ovum (quoted below), to Leuckart's elaborate analysis 

 (1. c., Bd. ii, s. 76-92), and also, especially, to the exhaustive 

 memoir of Claparede, whose brilliant labors, like those of Henry 

 Nelson, were too early terminated by death. Shortly after 

 graduation Nelson suffered a virtually enforced banishment from 

 his native land. 



BIBLIOGRAPHY (No. 33). Bellingham, 0. B., " On the Genus 

 to which the Worms known as Ascarides belong," f Dublin 

 Journ./ vol. xiv, 1839. Idem, " Catalogue of Irish Entozoa," 

 'Ann. of Nat. Hist./ vols. xiii and xiv, 1843-44; and in the 

 first part of Charles worth's ' Mag. of Nat. Hist./ vol. iv, 1840. 

 See also the address by Dr E. D. Mapother on the " Lives and 

 Writings of O'Ferrall and Bellingham," in the ' Dubl. Journ. 

 of Med. Sci./ Nov., 1877, p. 471 et seq.Bischof, < Widerle- 

 gung (u. s. w.)/ Giessen, 1853; quoted by Claparede, 1. c. 

 infra, p. 9. Idem, ' Bestatigung (u. s. w.)/ Giessen, 1864. 

 Idem, " Ueber Ei- und Samenbildung und Befruchtung bei 

 Ascaris mystax," Sieb. and Koll. ' Zeitsch./ 1855, s. 377; also 

 in S. and K. ' Zeitsch./ 1856. Bremser, ' Icones helminth./ 

 p. 23, tab. iv. Claparede, E., " Ueber Eibildung und Befruch- 

 tung bei den Nematoden," S. and K. ' Zeitsch./ 1857, s. 106. 

 Idem, ' De la formation et de la fecondation des ceufs chez 

 les vers Nematodes/ Geneve, 1859. See also f Ann. of Nat. 

 Hist./ vol. i, 3rd series, 1858. Cobbold, in ' Proceed, of the 

 Zoological Soc. of London,' Nov., 1862. Idem, ' Brit. Assoc. 

 Eep./ 1862. Idem, " On the occurrence of Ascaris mystax in 

 the Human Body," with figures, ' Lancet,' Jan., 1863; and in 



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