NEW MEGASCOLEX. 
101 
M. enormis, Fletcher, and M. attenuatus, Fletcher. The middle and 
hinder parts of the body represent, almost without any exception, 
the first step on the way to a complete perichaetine arrangement of 
the setae : six pairs of setae on each segment, being that state for 
which W. B. Spencer created the genus Trichceta (with six pairs of 
setae per segment throughout the whole body). The next step in 
the sequence from Notoscolex to the proper Megascolex is represented 
Fig. 3 .—Spermatheca of M. willeyi. 
From an acetic acid preparation ; enlarged. 
by the Ceylonese species Megascolex zygochcetus , Michaelsen, which 
has six pairs of setae at the second and third segments, and a greater 
number further back. 
Thus M. willeyi resembles Notoscolex at the head end, Trichceta at 
the tail end ; on the other hand M. zygochcetus resembles Trichceta 
at the head end, the proper Megascolex at the tail end. Regarding 
these relations, it must be admitted that I was justified in abolishing 
the genus Trichceta , which represents only an insignificant stage in 
the continuous series from Notoscolex to Megascolex . 
