710 The American Naturalist. [August, 
EMBRYOLOGY." 
Earthworm Phylogeny.—The great accumulations of anatomical 
facts that the study of exoti t has brought into existence dur- 
ing the past few years is now to be made more intelligible by the added 
facts of comparative embryology. It isa fitting tribute to one who has 
inspired so much of this recent exploration into this field that Bourne's 
paper upon the development and anatomy of certain Indian earth- 
worms should appear in the complimentary number of Lankester’s 
Quarterly Journal. 
When the study of exotic earthworms had shown that there might be 
large numbers of micro-nephridia‘ present in any segment and 
when it was even claimed that tubules of these micro-nephridia might 
anastomose to form a connection from segment to segment, the view of 
Lankester became less tenable as it became more probable that 
the ancestral condition of the earthworm was not what the common 
European earthworm had led one to expect. 
It seemed probable that the ancestor of the earthworm might have 
had a large number of nephridia and of setz and no definite segmental 
arrangement of these structures. 
. Now, however, we learn from Bourne's paper that in the development 
of Mahbenus imperatrix and Pericheta the vexatious micro-nephridia 
arise as out-growths from provisional mega-nephridia and are thus of 
apparent secondary value. The ancestral condition of a pair of 
nephridia for each segment being clearly indicated even in these cases. 
The connection of nephridial tubes, the so-called “ plecto-nephric ” 
condition does not, apparently, exist at all, certainly not in the embryo. 
We learn also that in these exotic forms, such as Pericheta (which is 
common with us in green-houses) the large number of setæ found in a 
band around each segment are not to be regarded as of ancestral value 
since they all arise from two germ bands that then give rise to matrices 
which grow laterally in each segment and form the numerous setal 
sacs by segregation of cells and by division of matrices. The setal 
germ bands in turn are regarded as probably arising from Wilson’s 
lateral teloblastes. 
Besides thus throwing much light upon the probable ancestral con- 
! Edited by E. A. Andrews, Baliimore, Md., to whom contributions may be 
sent 
” A. G. Bourne. Q. T. Mic. Anat., April, 1894. 
