ANATOMY AND CLASSIFICATION OF THE AKENICOLID.'R. 565 



Note the deeply notched ventral lip of the nephrostome, some of the blood- 

 vessels of which have blind dilated endings ; the dorsal lip fringed with 

 ciliated vascular processes ; and the secreting portion of the nephridium and 

 the bladder with tliis network of blood-vessels. The genital strand commences 

 on the inner side of tlie ventral lip of the nephrostome, and runs parallel to 

 and close to the secreting portion of the nephridium. Note also the sterile 

 strand of deeply staining cells on the ventral lip. Thegonidial vessel {G. V.) 

 runs axially through the genital strand. The large, flat, reniform lobe of the 

 testes is attached to the genital strand by a mesentery, through wiiich pass 

 branches of the gouidial vessel covered by genital cells {B. V. and Ge>i. C). 

 X 22. 



Fig. 49. — Section of the wall of the secreting portion of the nephridium of 

 a medium-sized specimen of A. ecaudata. The wall is formed by (1) columnar 

 secreting cells, the inner or free ends of which abut on the cavity of the 

 nephridium; (2) a small amount of almost homogeneous supporting tissue 

 situated at the bases of the secreting cells ; the nuclei of this tissue are shown ; 

 (3) a thin layer of coelomic epitiielium {Ccel. Epith.), immediately within which 

 are the blood-vessels (5. V.). The inner or free ends of the secreting cells 

 are very clear and free from granules. In many examples this clear portion 

 is much larger than in the specimen drawn. The outlines of the secreting 

 cells may be seen near their free ends, but they are not distinguishable towards 

 the bases of the cells. Tiie excretory granules present in the cells are of two 

 kinds : (1) those nearer the free ends of the cells, which stain black with htema- 

 toxylin ; and (2) those nearer the basal portions of the cells, which are yellow, 

 and do not stain with hsematoxylin. The latter are often aggregated into 

 heaps. They are drawn in red in the figure, but their natural colour is yellow. 

 X 570. 



Fig. 50. — A portion of the post-larval specimen of A. ecaudata shown in 

 PI. 24, fig. 35. The specimen was embedded in paraffin wax, and cut trans- 

 versely to the middle of the first nephridium. The remainder of the specimen 

 was cut longitudinally (sagittally) until the middle line, as indicated by the 

 nerve-cord, was reached. The portion then remaining was removed from 

 parafEn by immersion in warm xylol, and the half of the alimentary canal 

 remaining in the body of the worm dissected out. The body-wall and nephridia 

 attached to it were then mounted in cedar-wood oil. The preparation as it 

 now appears is shown in the figure. The left-hand side of the figure is dorsal, 

 the right-hand side ventral. A portion of the first nephridium was cut away 

 in the transverse sections. The other twelve nephridia are shown. On the 

 nephrostome of the second nephridium there is a small heap of cells the com- 

 mencement of one of the ciliated processes of the dorsal lip. The edo-es of 

 the nephrostome are thick, being formed of large columnar or cubical ceils. 

 The nephrostomes of the ninth and tenth nephridia are connected to the 

 secreting portion by narrow tubes 'OOS mm. and '01 mm. long respectively. 



