32 ALFRED GIBBS BOURNE. 
Fic. 16.—Urocheta sp. Secondary setal matrices of one side of the 
five segments a—e. v.v. Ventral median line. Ant. and Post. mark 
the anterior and posterior regions. 
PLATE 4. 
Fies. 17—32.—Pericheta pellucida; Fig. 33. Mahbenus im- 
peratrix. 
Figs. 17—21. Secondary setal matrices dividing before the appearance 
of sete. §. m. Secondary matrices. 7. m. Intermatricial bands. 
Cel. ep. Celomic epithelium. ep. HEpidermis. 
Fig. 22. Portions of the setal matrices of two consecutive segments with 
developing sete. In the lower portion of the figure which is anterior 
two new setz are shown developing between an older pair. 
Fig, 23. The entire setal matrices on one side of the body in three con- 
secutive segments. V. Ventral end. D. Dorsal end. Sete are seen 
developing in the most ventral and most dorsal regions, the former 
being the elder. 
Figs. 24 and 25. Later stages in the development of the secondary 
matrices. 
Figs. 26—28. Diagrams showing the exact number of sete on one side 
of the body in the segments marked 11, 111, Iv, &., in three embryos 
of different ages. V.V.and D. D. mark the ventral and dorsal median 
lines. 
Fig. 29. A similar diagram taken from an adult worm. 
Fig. 30. Portion of a matrix in which permanent sete are beginning to 
develop alongside the embryonic sete. 
Fig. 31. The complete seta ring of Segment 1 of an embryo 25 mm. long. 
The long fine lines represent the embryonic sets, the short thick lines 
the permanent ones. 
Fig. 32. The complete seta rings of Segments 11, 111, and Iv of an older 
embryo from which the embryonic sets have nearly all dropped in 
these anterior segments; those left are shown by the small fine lines, of 
which there are 6, 12, and 19 in the different segments. 
Fig. 33. An embryo of Mahbenus imperatrix showing the entire 
series of nephridia, The references Weph. 1, Neph. 2, &c., are con- 
nected with the excretory ducts; the excretory pores themselves are 
within the limits of the preparation in the case of nephridia 7 back- 
wards. S. m. Setal matrices. Sep/. Septa torn during the removal 
of the alimentary wall. 
