47 118 



Proceedings of the Royal Irish Academij. 



rounded points. In some of the feet the lowest crochet shows traces of a 

 cleft at the tip, but no distinctly bifid setae were seen (fig. 29k). 



No trace of genital products was seen in this specimen. 



The characteristics of the three stages may now be tabulated, so as to 

 make the comparison clearer : — 



SlAGli A. 



1. Taken only in the sur- 



face tow-net at night. 

 Found, from March- 

 August. 



2. Length 4-6 mm. 



3. Number of segments 



36-64. 



4. Body inflated in the 



anterior region, with 

 cylindrical posterior 

 end. 



Stage B. 



Stack C. 



5. Head with pair 

 lateral CVCS. 



of 



G. Borsal branchiae on seg- 

 ment in front of that 

 healing the setae. 



7. Setae 5-8 in number in 

 each division. 



Living in clean sand. 

 Found in September. 



Length 11 mm. 

 Number of segments 120. 



Body cylindrical, with 

 slight flattening of pos- 

 terior end. 



Head with pair of ventro- 

 lateral ly placed eyes. 



ltesemblcs Stage A. 



Setae 7-9 in each division, 

 longer and more promi- 

 nent than in Stage A. 



8. Crochets absent from Crochets absent from dor- 



dorsal divisions. sal divisions. 



9. The majority of the j Crochets not so distinctly 



crochets distinctly hi- ' bifid as in Stage A. 

 fid, but the upper 

 crochet with simple 

 tip. 



Living in clean sand. 

 Pound in March. 



Length 44 mm. 



Number of segments 150. 



Body cylindrical in front, 

 with marked flattening 

 of posterior end. 



Head with pair of ventially 

 placed eyes. 



Bescmbles Stage A. 



Setae 18-25 in each divi- 

 sion, longer and more 

 prominent than in Stage 

 A or B. 



Crochets absent from dorsal 

 divisions. 



Crochets with simple 

 rounded tips. Only ex- 

 ceptionally the lowest 

 crochet shows indication 

 of a bifid tip. 



It will thus be seen that the three stages resemble each other in the 

 shape of the head, the position of the dorsal branchiae, the arrangement of 

 the setae, the absence of crochets from the dorsal divisions of the feet, and 

 the general shape of the setae. The chief differences between Stage A and 

 Stage C relate to the size, number of segments, shape of the body, and the 

 nature of the tips of the crochets. In all these characters, Stage B seems to 



