24. ALFRED GIBBS BOURNE. 
Embryonic sete. Permanent sete. 
Segment 11 : : a ; : 35 
5 III : ; 1D: ee : : 40 
Bs IV : : 19 «tC : ; 40 
3 Vv “ - Zou ts : : 50 
- VI 3 ; Biey ; : 36 
Jai By at : ; a9... : ; 27 
5) WIIL ; : 40. ; ; 26 
55 IX . ‘ 48 ‘ ; 12 
ss x 5 : 52a ‘ ; 2 
ads XI : . 44, 5 3 0 
The seta rings of Segments 11, 111, and 1v of this worm are 
shown in fig. 32. 
3. Embryo 40 mm., embryonic setz down to CLxXxxvi, the 
number of embryonic and permanent sete as under: 
Embryonic sete. Permanent sete. 
Segment 11 . : 1 ie : : 32 
s III ; : YB) oe ; : 42 
a IV ‘ 4 40. : : 48 
aI Vv : : 30... ‘ : 32 
. VI 
i bi . 40 t0 50. . few and very small 
” Ix 
= x and onwards . ; 4 : none 
This embryo was much more backward in regard to its seta 
development ; it had not lost so many embryonic sete nor deve- 
loped permanent sete to such an extent as had the others, 
NEPHRIDIA. 
Development of the Nephridia in Mahbenu 
imperatrix. 
I propose to deal here with certain stages only in the de- 
velopment of these organs—the stages which have a special 
bearing upon the so-called “ plectonephric” condition. I deal 
chiefly with Mahbenus imperatrix. All my observations on 
the early stages corroborate those of Vejdovsky, and the later 
