OPISTHOBRANCHIATA OF BRAZIL 



cerata than the posterior one, the number in both decreasing in 

 each group from the first backward, until the posterior limb 

 entirely disappears, the anterior row being alone represented in 

 the groups from the sixth onward. In figs. 90 and 91 the 

 bases of the cerata are outlined by small circles, indicating the 

 relative size and positions of these groups. The number does 

 not exactly correspond upon the two sides of the body for each 

 group, but the difference is not marked, the total number for the 

 right side being eighty, that for the left eighty-one. The distri- 

 bution of the cerata in the anterior and posterior limbs of the 

 groups is shown in the following tabulation. 



These figures may be expected to vary somewhat in individ- 

 uals of different sizes, as they do also for the Mediterranean 

 species. 



The anterior limb of the first group begins in front of and 

 below the bases of the rhinophores. The reproductive openings 

 are situated close together, below the first arc of cerata on the 

 right side; the anal opening is placed on a prominent tubular 

 papilla, well up on the same side, and is included in the span 

 of the second group. The opening is large, with slightly lobulated 

 margins (PI. XVI, fig. 88). The very minute renal opening is 

 immediately in front of its base. 



