214 CLASS VII. 
colour shining through the skin, which is white in male individuals 
and reddish in female. Other differences of external appearance 
in the two sexes are not known, unless we except an observation of 
OeErstED, which however is not altogether free from doubt, accord- 
ing to which in a new genus very nearly allied to Syllis, which he 
names Hxogone, the male individuals are distinguished by longer 
hairs, as they are in the genus Nois!. There still remain the 
genera of the Hirudinea and Lumbricint, in which STEENSTRUP in- 
deed adopts separation of sex under similar external form of the 
parts: but this requires confirmation after accurate investigation, for 
it is in conflict with earlier observations, whilst by later it is in part 
contradicted2. On the whole, no common type can be assigned for 
the genital organs: for the most part, there are some pairs of vesicles 
(ovaria, testes) in the fore part of the body. In some Annulata setigera, 
apertures at the base of the foot-swellings have been seen, through 
which passes seed or eggs: but in many of them such an outlet is still 
unknown. For the most part, external genital organs are deficient : 
neither does copulation occur, except in Lumbricinié and Hirudinea. 
The development of the egg has been investigated only in a 
few species. Here also that remarkable cleaving and successive 
division of the yelk has been observed, which Rusconr and Von 
Baer first detected in the eggs of frogs and of fishes. The deve- 
lopment of the embryo begins on the abdominal surface, and the 
yelk lies on the dorsal surface, as in Crustaceans and Insects: two 
abdominal streaks are observed at the commencement of develop- 
ment, which recall the dorsal plates of vertebrate animals*. 
The most recent times have made us acquainted with some 
remarkable metamorphoses in the course of the development of 
ringed-worms. LOVEN found the first stage in a worm of the 
family of the Nereids (probably a species of Phyllodoce) to resemble 
1 Ericuson’s Archiv f. Naturgesch. 1845, 1. 8. 20—23. 
2 See F. Murnier on the Hermaphroditism of the Hirudinea, in the German 
translation of STEENSTRUP’S work cited above (p. 135) Untersuchungen ueber das 
Vorkommen des Hermaphroditismus in der Natur. Greifswald, 1846, s. 110—114. 
3 Most of the observations refer to Hirudinea. Such are the following works :—— 
E. H. Weser, Veb. die Entwickelung des medicin. Blutegels, MECKEL’S Archiv. 1828, 
s. 366—418, Taf. x. x1.; R. Wacner, Bruchstiicke aus der Entwickelung des gemeinen 
Blutegels, Hirudo vulgaris L., Nephelis tesselata Sav. OKEN’S Isis, 1832, s. 398—408, 
Taf. v.; A. E. Gruse, Untersuchungen ucber die Entwickelung der Clepsinen. Mit 3 
Kupfert. Kénigsberg, 1844. We may expect several observations on marine annulata 
from QUATREFAGES. See Ann. des Sc. nat. 3ivme Série, Zoologie 1. p. 21. 
