540 - FLORENCE BUCHANAN. 



to be a new species of Sabella. The change of setae in three 

 of them takes place between the eighth and ninth segments. 

 In one specimen, however, there are nine pairs instead of 

 eight thoracic parapodia, and the change on the left side takes 

 place distinctly in front of the ninth ventral shield, whereas 

 that on the right takes place distinctly behind it (fig. 8). This 

 is accounted for by the fact that the second ventral shield is 

 divided on the left side, and there is a separate parapodium to 

 each half. Thus in taking a ventral view of the animal we 

 ■see what appears to be a spiral beginning in the third half- 

 segment on the ventral surface, left side, and going on into the 

 abdomen to end (?) in the hundred and second segment on the 

 ventral surface, right side, about twelve segments before the 

 end of the body. The reason why one cannot say with absolute 

 certainty that this is a case of spiral segmentation is that the 

 segments are not marked off from one another on the dorsal 

 surface, and one cannot therefore trace them right round the 

 body. But the ventral view of the animal shows exactly the 

 condition which obtains throughout the length of any spiral 

 beginning and ending on the same surface in the other 

 Chsetopods. If it is a spiral it is a right-handed one, and 

 remarkable for its length. I cannot be quite certain of its 

 ending in the hundred and second segment, as the segments at 

 the posterior end of the body are extremely narrow and very 

 difficult to follow ; but it certainly does not end before, at least 

 not on the ventral surface. 



Before leaving the subject I should like to draw attention to 

 the existence of spirals similar to those we have been consider- 

 ing in another group of animals altogether. In a recent 

 number of the ' Quarterly Journal of Microscopical Science' 

 (vol. xxxiv, 1892) Baldwin Spencer, in describing the female of 

 Pentastomum teretiusculum, Baird, says that there 

 are occasionally incomplete segments wedged in on one 

 side or the other between the complete ones. He figures 

 one specimen with two of these so-called wedges, but to 

 me it looks very mucii as though there were a spiral 

 going tour times round the body (i. e. between his two 



