208 DESCRIPTIONS OF PREPARATIONS. 



vesicle : the oviduct of all, and vasa deferentia of Lumbricus, &c. to the nephridial 

 tube) : and that they are excretory organs developed only at the time of sexual 

 maturity. In the lower Oligochaeta the sexual apparatus atrophies after the sexual 

 products are discharged, but the worms appear to live on and may propagate 

 themselves asexually. It is probable that the development of the sexual apparatus 

 of the Earthworms will be found to be similar to that of the aquatic Oligochaeta. 

 The only thing that must be regarded as certain at present is the fact that the 

 sexual ducts of Oligochaeta are not, as in many Polychaeta, ordinary nephridia, 

 which take on a sexual function at the reproductive season. It is possible that 

 the resemblances traceable between them and the nephridia are merely homo- 

 plastic 1 and not homogeneous : i. e. the structures may not be identical. And the fact 

 that the vasa deferentia of the Earthworms extend through several somites before they 

 open externally may be held to support this view. It is true that the nephridia of 

 the aquatic Phreatothrix extend through several somites. They form, however, 

 U-shaped tubes and their external and internal apertures are always in two con- 

 tiguous somites as in other Oligochaeta (Vejdovsky, op. cit. p. 124). 



The terrestrial Oligochaeta do not multiply by fission and gemmation as do 

 many of the aquatic forms. They appear, however, to have considerable powers of 

 regeneration : and can form new anterior and posterior somites, supra- and sub- 

 oesophageal ganglia, and pharynx in the place of parts removed by excision. 

 They have been occasionally found with a bifid posterior extremity. 



Digestive tract. Claparede, op. cit. ante, p. 600 ; in general, Vejdovsky, op. 

 cit. pp. 100-112. Chloragogen cells, Vejdovsky, op. cit. pp. 110-112. Secretion of 

 calcigerous glands, Robinet, C. R. 97, 1883. Digestive ferments. Krukenberg, Unter- 

 such. Physiol. Inst., Heidelberg, ii. 1882, p. 37 ; Fredericque, Bull. Acad. Belg., 

 (2) 47, p. 217. Colouring matter from intestine. MacMunn, Proc. Philos. Soc., 

 Birmingham, iii. 1881-3, P- 3^9- 



Vascular system. Jaquet, Mitth. Zool. Stat. Naples, vi. 1885 ; Vejdovsky, 

 op. cit. pp. 1 1 2-1 20. Double dorsal vessel. Beddard, Proc. Roy. Phys. Soc., Edin- 

 burgh, 1885. Blood and blood corpuscles. Vejdovsky, op. cit. p. 118; Ray 

 Lankester, Q. J. M. xviii. 1878, p. 72; Blomfield and Bourne, Q. J. M. xxi. 

 1 88 1. Endothelium of vessels. D'Arcy Power, Q. J. M. xviii. 1878. Coelomic, i.e. 

 amoeboid cells. Kiikenthal, J. Z. xviii. 1885. 



Nephridia. Claparede, op. cit. ante, p. 615; Gegenbaur, Z. W. Z. iv. 1853. 

 In general and development. Vejdovsky, op. cit. pp. 120-129. Of Acanthodrilus 

 multiporus. Beddard, A. Sc. N. (6)xix. 1885. Of a N. Z. Acanthodrilus. Id. Z. A. 

 viii. 1885. 



Sexual organs. Hering, Z. W. Z. viii. 1856-57 ; Bergh, Z. A. ix. 1886. In 

 general and development. Vejdovsky, op. cit. pp. 125-151. Development of sperma- 

 tozoa, vesiculae seminales. Blomfield, Q. J. M. xx. 1880; cf. Jensen, Archives -de 

 Biol. iv. 1883. Spermatophores. Fraisse, Arb. Zool. Zoot. Inst., Wurzburg, v. 1882; 

 Vejdovsky, op. cit. p. 154. Accessory organs. Vejdovsky, op. cit. p. 135. Homo- 

 logies. Id., op. cit. pp. 157-161. 



Regeneration of excised parts. Miss Fielde, Proc. Acad. Nat. Sc. Philadelphia, 

 pt. i, 1885; cf. on Lumbriculus, Billow, Z. W. Z. xxxix. 1883. Bifid Earthworms. 



1 For 'homoplasy,' see Ray Lankester, 'Use of the Term Homology,' &c., A. N. H. (4) vi. 

 1870. 



