424 



DR S. F. HARMER AND DR W. G. RIDEWOOD ON THE 



flexure has taken place; and in the later sections of the series (fig. 11), the arm is 

 seen in transverse section as a continuation of the part marked R. 8 The elongated 

 part which stretches from this region towards the ninth arm shows the food-groove 

 (R. 8 *) opened out and cut obliquely at or near its flexure. 



The eighth left arm (figs. 11-8) also has its food-groove directed posteriorly; but 

 it lies in such a position that it is cut almost longitudinally as it passes across the 

 dorsal side of the principal part of the collar. The ninth left arm (figs. 10-6) at first 

 lies between the eighth arm of the same side and the region of the central nervous 

 system (figs. 10-8). It runs more or less horizontally near its base, but soon curves 

 dorsally, so as to appear even in the first section (fig. 6) which has been represented. 



Although there are eighteen arms in the zooid which has thus been described in 

 detail, this number is not constant in the species. A series of selected zooids were 

 dissected and were found to give the results set forth below. It is possible, however, 

 that arms may have been lost in some of the zooids examined, either by accident 

 during life or as the result of violent contraction at the moment of preservation, and 

 that some margin of error may thus have been introduced into the table. The facts 

 as observed are as follow : 



If it may be inferred that in a zooid with thirteen arms, for instance, there were 

 seven arms on one side and six on the other, it follows that of the forty individuals 

 dissected there were only three which had less than seven arms on one side at least, 

 and these appear to have had six pairs. In four cases there were seven arms on one or 

 both sides ; in fifteen cases there were eight arms on one or both sides ; in seventeen cases 

 there were nine arms on one or both sides ; and in one case there were ten arms on one 

 side. Representing these as percentages, it follows that the observations indicate : 



(ROY. soc. EDIN. TRANS., VOL. XLIX., 548.) 



