536 FRANK E. BEDDARD. 
provided with a funnel which opens at the segment in front. 
They are present in all the segments of the body, but there is 
only one pair of nephridia to the first two segments. These 
latter open on to the exterior at the commencement of the 
stomodeum. Later the second pair of nephridia, and after- 
wards one or two other pairs, become connected with the first 
pair, and collectively constitute the “mucous gland ;” the 
stomodal opening of this gland has moved further within 
the stomodeum. The funnels of the nephridia, except those 
belonging to Segments 11—14, become rudimentary, and 
numerous secondary external apertures are formed. The anal 
nephridia are a comparatively late formation ; they appear to 
open into the mesenteron, not into the proctodeum. 
(2) Gonads.—There are four pairs of gonads, which up to 
a certain point develop equally ; later the gonad of Segment 
12 degenerates. 
(3) Genital Ducts.—Four pairs of genital ducts are deve- 
loped ; they are formed out of the nephridial funnels and a 
short section of the following tube: the genital ducts belong- 
ing to the 12th segment degenerate. 
(4) The young embryo is furnished with an unpaired sense- 
organ consisting of a few large ciliated epidermic cells to one 
side of the stomodzal aperture; this is not recognisable in 
later stages. 
(5) In the epidermis of the very advanced embryo there are 
peculiar cells which may possibly be sense-organs ; the cells 
lie immediately beneath the cuticle, and are separated by a 
space from the basal membrane of the epidermis. 
