Fisslparous Species of Tubicolar Annelid. 125 



germinal spot. By degrees they increase in size to F £ ff inch, 

 with a germinal vesicle of toWj an( i a S P ^ °f ssVo-s an( i a few 

 granules become visible in their yelk. From this size they 

 gradually increase to the r £o i ncn m diameter, acquiring a 

 well-marked vitellary membrane, and a dark orange-red, very 

 coarsely granular yelk. The germinal vesicle and spot may 

 still be rendered visible by pressure, the former having about 

 e <yo °f an i ncn ' m diameter. 



When those segments of the body in which the genitalia 

 are situated were subjected to moderate pressure, the sperma- 

 tozoa made their exit at the bases of the pedal tubercles of the 

 male segments, while the ova, just giving rise to bulgings in 

 a corresponding position, eventually passed out in the same 

 manner. I could not satisfactorily decide, however, whether 

 the apertures by which the generative products passed out 

 were natural or artificial.* 



Setce and Uncini of the Pedal Tubercles. — The general 

 form of the pedal tubercles has already been described ; it re- 

 mains only, therefore, to note more particularly the form of 

 their appendages, whether Seta} or Uncini. The Setm (figs. 7, 8) 

 are slender spines, about ^ of an inch in length, consisting of 

 a haft and a blade ; the former is about six times the length of 

 the latter, and is rounded, flattening gradually as it passes 

 into the blade, with which it is completely continuous, though 

 at an obtuse angle. t The blade tapers gradually to its point, 

 and is smooth on one edge, but minutely denticulated upon 

 the other, while delicate striae are continued from the serra- 

 tions upon the flat face of the blade. 



Such is the structure of those stronger setae which are di- 

 rected forwards on each side of the head-lobe. Those of the 



* It should be added that the genital products occupy about fourteen suc- 

 cessive segments of the abdomen, of which the two anterior are seminiferous ; 

 the rest, ovigerous. See fig. 3. 



t I am not aware of any annelid in which the setae are really articulated. 

 The statements of Audouin and Milne-Edwards rest, I believe, upon errors of 

 observation, very intelligible, if one considers what microscopes were twenty 

 years ago. How such strange perversions of fact as the figures of annelid 

 setae appended to Dr Williams's Report on the British Annelida, published in 

 the Transactions of the British Association for 1851 — can have arisen, it is 

 not so easy to comprehend. 



