200 DESCRIPTIONS OF PREPARATIONS. 



number of setae in each somite is also not constant. Among Earthworms Lum- 

 bricus has a pair in each of the four longitudinal rows (i. e. eight) in each somite. In 

 some species of Acanthodrilus, in Titanus, the eight setae are sometimes separated 

 by equal intervals, and there are consequently eight rows, i. e. four on each side. 

 The eight setae when thus separated may not remain in line from somite to somite, 

 but alternate in position, as in the posterior somites of Urochaeta. Megascolex has very 

 numerous setae, interrupted only in the median dorsal and ventral lines, whereas in 

 Perichaeta and Perionyx single setae are implanted at intervals round the circumfer- 

 ence of each somite. It is difficult to say whether the concentrated or scattered mode 

 of distribution is the more primitive (see under nephridia, p. 205). The genus Acan- 

 thodrilus affords an instance of variations in this particular in different species. 



The clitellum of Earthworms appears to fulfil two functions. It is a copulatory 

 organ, and in L. foetidus Perrier observed the formation of a resistent membrane 

 from its surface during sexual congress. It also secretes the cocoon in which the 

 ova are contained together with spermatozoa and albumen. The cocoon is stripped 

 oft forwards by contractions of the body : and is charged with its contents in tran- 

 sit (?). The two ends of the cocoon close of their own accord as soon as it is freed 

 from the body. In some Earthworms the clitellum surrounds the body, and there 

 is no ventral furrow, as occasionally happens in L. terrestris. Its position and extent 

 are variable not only in different groups of terri-colous Oligochaeta, but within cer- 

 tain limits in the same genus and even the same species. In the aquatic Oligochaeta 

 it includes only the somite in which the vas deferens opens, and it does not secrete 

 during congress. It is apparently absent in Moniligaster among terrestrial Oligochaeta. 



Phosphorescence has been noticed in various Lumbrici, and appears to be due 

 to a fluid excreted from the hypodermis (see Vejdovsky, p. 67). 



System und Morphologic der Oligochaeten, Vejdovsky, Prague, 1844. Id., 

 Monographic der Enchytraeiden, Prague, 1879. Lombririens Terrestres, Perrier, 

 Nouvelles Archives du Museum d'Hist. Nat. de Paris, viii. 1872. Studies on Earth- 

 worms (first of a series), Benham, Q. J. M. xxvi. 1886. 



Lumbricus terrestris. Claparede, Z. W. Z. xix. 1879 ; Horst, Tijdskr. Neder- 

 land. Dierk. Vereen, iii. 1876 ; cf. A. N. 43, (ii), 1877, p. 481 ; Brooks, Handbook of 

 Invertebrate Zoology, Boston, 1882, p. 140; Howes, Atlas of Practical Elementary 

 Biology, London, 1885. 



Plutellus, Perrier, A. Z. Expt. ii. 1873. Urochaeta, Id. op. cit. iii. 1874. 

 Pontodrilus, Id. op. cit. ix. 1881. Megascolex (= Pleurochaeta) Moseleyi, Bed- 

 dard, Trans. Roy. Soc. Edinburgh, xxx. pt. 2. Megascolex, Perichaeta, Id. A.N.H. 

 (5), xiii. 1884. Do. with Perionyx and Typhaeus, 'Earthworms from India,' Id. op. 

 cit. xii. 1883. Perichaeta, Moniligaster, ' Earthworms from Ceylon,' Id. op. cit. xvii. 

 1886. Acanthodrilus capensis, Id. Proc. Roy. Soc. Edinburgh, 1885. Micro- 

 chaeta Rappi, Id. Tr. Z. S. (to appear) ; and Benham, op. cit. supra. 



Hypodermis. Von Mojsisovics, SB. Akad. Wien, Ixxvi. Abth. i. 1877 ; Ray 

 Lankester, Q. J. M. xx. 1880, p. 303. Body wall. Beddard, Proc. Roy. Soc. 

 Edinburgh, 1884. Muscles. Rohde, Schneider's Zool. Beitrage, Breslau, i. 1885. 

 Dorsal pores and musculature. Ude, Z. W. Z. xliii. pt. i. 1885. Peritoneal epithelium. 

 D'Arcy Power, Q. J. M. xviii. 1878. 



Cocoon and congress. Perrier, A. Z. Expt. iv. 1875, notes, p. xiii. ; cf. Ratzel, 

 and Warschawsky, Z W. Z. xviii. 1867-69, p. 547. 



