76 ARENICOLA BCAUDATA. 



Mesnil. A hook indistinguishable from the ventral occurs in some of the posterior tufts 

 of bristles, and this was also found by Mesnil in the form just mentioned. 



There are thirteen pairs of nephridia, viz. from the fifth to seventeenth setigerous 

 rings. They resemble those of A. branchialis, except that the funnel is often narrower 

 from side to side, and the dorsal lip bears a greater number of processes. All have 

 gonads. The bladder is generally larger. Ripe ova in the females often accumulate in 

 the vesicle so as to make a thin walled sac — like an outgrowth of the vesicle. 



Reproduction. — Gamble and Ashworth state that they breed in spring (April at Port 

 Erin). 



A large female from Great Aran Isle (Dr. Scharff) in September was taken with large 

 thick-shelled ova, and Dr. Ashworth mentions that he had ripe examples from Plymouth 

 at the end of August. Fauvel found the period range from March to October. 



Ovaries and testes are so voluminous as to conceal the greater part of the segmental 

 organs and the alimentary canal. In the male the gonad is a capacious sac, in the female 

 a tuft of follicles. The gonads are larger, more complicated, and more numerous (twelve 

 pairs) than in A. branchialis. The strands of the first pair of segmental organs do not 

 give rise to gonads. The ova are retained in these till almost ripe, and thus they differ 

 from those of other species. In their long diameter the ova are 0*13 mm. to 0*14 mm. and 

 have a thick vitelline membrane. The male genital cells fall from the testes after two or 

 three divisions and complete the development in the ooelomic' fluid. Gamble and Ashworth 

 found in August, in the roots of Laminaria, young examples from 7*2 mm. to 9*4 mm. 

 which they considered only a few months old. They had thirteen pairs of segmental 

 organs, but no gills. Fauvel (1899) shows that these young live amongst algse in a 

 gelatinous tube, only later when the gills are well-developed do they live in sand. 



The smallest example procured between tide-marks at Lochmaddy (August, 1865) 

 measures in spirit about 4 mm. in length, but it would probably stretch considerably more 

 in life. No branchia3 are present. Moreover the body does not show the abrupt narrowing 

 of the caudal region behind the bristles so characteristic of the pelagic young of A. marina 

 procured in the bottom-net. The anterior rings are wide, whilst the posterior are 

 numerous and narrow. There are between fifty and sixty bristled segments. 



The next stage is represented by a specimen about 7 mm. in length, also obtained 

 between tide-marks at Lochmaddy. In front of the first bristle-tuft are the somewhat 

 large blunt prostomium, and five rings. The setigerous lobes are distinct, and the first 

 gill arises on the sixteenth. As the anterior segments are much broader than the posterior 

 the branchial region occupies nearly half the length, and is characterised by a deep 

 furrow on the dorsum of the preparation. In the anterior half a single ring is inter- 

 polated between the setigerous lobes, but the feet are so crowded posteriorly that no more 

 than one ring to each is present at this stage. The branchiae (more than forty pairs) are 

 for the most part simple filaments, or a pair of filaments, and they appear to be longest 

 anteriorly. The bristles are proportionately larger than in the adult and have a trace of 

 a wing on each side. The anus is median and papillose. 



The third stage, also obtained in August, is about 11*5 mm. in length and the same 

 general shape is maintained. The gills commence as a small simple process on the 

 fifteenth segment, and a longer slightly branched organ on the sixteenth. About forty 



