THE GIANT EARTH-WORM OF GIPPSLAND. 39 
ccelomiec space. Whether it is an entirely new structure, or developed as a 
modification of a pre-existing flame cell, it is quite impossible to say definitely, 
though the simplicity of the structure in such leeches as Clepsine may perhaps 
indicate its development from a flame cell, more especially if, as suggested by 
Hartoe,* a flame cell be really an internally ciliated cell. 
The segmental arrangement of the network, almost absent in Branchellion, and 
indicated in Pontobdella, is carried to a much greater extent in other leeches, the 
segmentally arranged portions losing their connection with each other, and each one 
acquiring its internal and external openings. The ducts, though aggregated into a 
definite tubular structure, still lie embedded in the mesodermic tissue, only their 
internal funnels lying freely in the ccelomic spaces, and having short tubes which 
connect them with the ageregated portion of the network. In Hurudo itself there 
still persists a part which Bourne regards as the remnant of a formerly existing 
connection between one nephridium and another. 
The stages of development in AHirudinea may be, briefly, somewhat as 
follows :— 
(a) A complete network of tubules (certainly at first with “flame cells,”) and 
with posterior openings, and no, or only the faintest, trace of segmental arrangement. 
Such a stage is now possibly seen in Branchellion. 
(6) A complete network of tubules, with paired external openings, and internal 
ciliated funnels opening into definite coelomic spaces. This stage is now seen in 
Pontobdella. The internal openings may be developed by modification of pre-existing 
flame cells, or be entirely new formations. 
(c) An aggregation of the network into portions segmentally arranged, forming 
definite paired nephridial tubes, each independent of the others, and with its own 
internal and external openings. This now exists in the adults of most leeches, as 
Hirudo and Clepsine. 
2.—Inthe Chetopoda. An important difference in the nephridia of this group, 
as compared with those of Hirudinea, seems to have been brought about by the 
development of much larger and more extensive spaces within the mesoderm, which 
have moreover a segmental arrangement, and but very little lmear connection with 
each other. 
Taking the group as a whole, we find two sets of structures present in connection 
with the nephridial system :— 
(a) A network of tubules in the body wall, and hence embedded in mesoderm. 
(b) A series of regularly or irregularly arranged coiled tubes depending from (a) 
into the successive ccelomic chambers. With them may, or may not, be associated 
definite nephridial funnels. 
* Ann. Mag. Nat. Hist. 1887. P. 326. 
