ON THE SEXUAL PHASE IN CERTAIN OF THE NAIDID^. 795 



The ampulla of the spermatheca can again be divided into two portions, an outer 

 (i.e. nearer the exterior, and communieating with the duct) and an inner. The 

 outer portion is a small ovoid chamber, fairly constant in size in the different 

 specimens, lined by a well-marked epithelium of a low columnar, almost cubical type, 

 the cells having spherical nuclei larger and much less close together than in the 

 duct. This is continued upwards into the inner portion, which is distinguished 

 by having thinner walls, and by being much more variable in size and shape than 

 the parts of the spermathecal apparatus already considered. The whole ampulla, 

 inner and outer portions together, has a more or less sausage-shaped form, or some- 

 times resembles a bent finger ; the innermost portion may be considerably dilated. 

 Its terminal blind end lies some distance below the dorsal body-wall, and as a rule, 

 owing to the backward curve of the ampulla, in the hinder part of the segment, 

 near septum 5/6 ; or, stretching further back still, it may enter the mouth of the 

 sperm-sac. The thickness of the wall of this inner portion of the ampulla varies ; 

 it is less than that of the outer portion, and may indeed be much attenuated ; it 

 may vary from one part of the circumference to another in the same section. The 

 muscular and peritoneal investments are much thinned out. 



Penial seise occur at the male aperture. They are the ventral setae of 

 segment vi, which at this period present special characters (fig. 5). They seem 

 to be usually one on each side ; in one specimen one of the bundles contained three. 

 They are 96 ^ in length (the setse of the next succeeding segment in this case measured 

 125 m), and end distally in a single hook ; there is no distinct nodulus, but the shaft 

 is thickest one-third to one-quarter of its length from the distal end. 



EXPLANATION OF PLATE LXXX. 



Figs. 1 and 4 semi-diagrammatic ; 2 and 3 drawn by means of Abbe's drawing apparatus (Zeiss). 



Fig. 1. Dero limosa; genital region. x' ca. 120. Amp., ampulla of spermatheca ; air., atrium; 

 clit., clitellum; d., duct of spermatheca; /., male funnel; p., peritoneal cells; ov., ovum; ovis., ovisac; 

 s.s., sperm-sac; v.d., vas deferens; $ , male aperture. 



Fig. 2. Dero sp. ; anterior end of sexual specimen, showing commencing degeneration of alimentary 

 canal. x 100. Atr., atrium; b.c, buccal cavity; e.g., cerebral ganglion; clit., clitellum; d.v., dorsal 

 vessel; /., male funnel; ?n., muscular layer of body-wall; m.ap., mouth aperture; ph., pharynx; 

 ces., oesophagus ; spth., spermatheca ; v.n.c., ventral nerve cord ; v.v., ventral vessel. 



Fig. 3. Dero limosa ; anterior end of sexual specimen, with advanced degeneration of alimentary canal, 

 x 160. The muscular coat has separated from the epithelium in the region in front of the clitellum; the 

 large mass of cells dorsally on the cerebral ganglion are probably wandering cells, not nerve cells. Lettering 

 as for fig. 2. 



Fig. 4. Slauina punjabensis ; genital region. x ca. 100. The atria are naturally one on each side of 

 the single sperm-sac, which is a diverticulum of septum 5/6. The ovary is shown, attached to septum 

 5/6, near the lower part of the vas deferens. Lettering as for fig. 1. 



Fig. 5. The same; genital seta. x 550. 



