Genus Megascolex of Templeton. 399 
serve to clearly differentiate the two. Templeton’s original 
notice of Megascolex ceruleus is contained in a letter read 
before the Zoological Society of London in 1845* ; but the 
facts given chiefly relate to certain external characters and 
are not at all sufficient to determine the systematic position of 
the earthworm. The sete are stated to be arranged in a con- 
tinuous ring round each segment, except in the mesial line 
of the back, where they are altogether wanting, while the 
generative organs occupy segments 16, 17, 18. The latter part 
of the description is too vague to be of any use, since it is not 
clear what is meant by “ generative organs,” whether the 
testes and ovaries, their external apertures, or, finally, the seg- 
ments upon which the clitellum is developed. Schmardat 
distinguished his genus Pericheta mainly by the arrangement 
of its sete; his generic definition is as follows :—“‘ Sete 
totam segmentorum circumferentiam in forma annuli cin- 
gentes.”” He mentions Templeton’s genus MJegascolex as 
having the setee developed only upon the back, and, in fact, 
entirely reverses the account of the arrangement of the sete 
given by Templeton; the “ generative organs” of ‘Temple- 
ton’s description Schmarda interprets as the clitellum. In 
1869} Baird examined the type specimens of Megascolex ceru- 
eus in the British Museum, and came to the conclusion that 
there was no difference of importance (indeed no difference 
at all, except size) between that genus and Pericheta, The 
only structures, however, which he seems to have compared 
with any care in the two forms are the sete; and these are 
precisely the very worst characters that could have been chosen 
to determine such a question. Itis impossible to arrive at pny 
corrée. notion about the systematic position of an earth’. orm 
without an examination of its internal structure and the rela- 
tions of the male generative apertures to the clitellum. Vail- 
lant §, and afterwards Perrier||, more fully demonstrated the 
importance of the latter character; and Perrier has suffi- 
ciently shown how earthworms, similar in external characters, 
may differ most widely in their anatomy; moreover Baird’s 
figures of the sete ot Megascolex caruleus and Pericheta 
diffringens do show some slight differences, quite enough to 
distinguish them if it were at all possible to make use of such 
a trifling external character. Baird makes no statements at 
all about the clitellum and generative pores in Megascolex. 
* P.Z.S. 1845, p. 89. 
+ Neue wirbellose Thiere (Leipsic, 1861), Bd, i. 2. 
t P.Z.S. 1869, p. 40. 
§ Ann. Sci. Nat. loc. cit. 
|| Nouv. Arch. &e. doe. cit. 
