82 ART. 4. — N. YATSU : 



not show any difference from those of the cirri (PI. VII., Figs. 

 91, 93). 



The cirri are constantly budded out on each side of the base 

 of the tentacle, or more strictly speaking, on the ventro-lateral 

 sides of the latter. In the larvœ now under consideration only 

 nine pairs are formed, — an insignificant number compared with 

 the several thousands that are found in the adult, At its first 

 appearance a cirrus is like a little hillock, which elongates with age, 

 until it attains a length of about 30 /". In the position of rest it is 

 bent upon itself and the more ventrally a pair is situated, the 

 nearer the point of bending comes to the base of the cirri. 

 Structurally each cirrus is a hollow tube, its diameter being in most 

 cases less than that of the tentacle (PL VI., Fig. 84), and its walls 

 being formed of a thick epithelium, whose nuclei are arranged 

 compactly and take an intense stain. The latter are most numerous 

 on the inbent side of the cirrus, while on the outer curved side they 

 occur sparingly (PI. VII., Fig. 121). In life the cirrus is covered 

 uniformly with long cilia, those at its tip being the longest. The 

 lumen in the cirrus (cirrial canal) (cr. en.) runs nearer the inner 

 side than the outer, and stops short at the tip, leaving there for 

 a short distance a solid part (PI. V., Figs. 77-79). The cirrial 

 canal is lined with a thin epithelium as in the tentacular canal 

 (PI. VIL, Fig. 121). On the inner side of the cirrus, between 

 the outer epithelium and the inner lining, a layer of muscle 

 fibres, which run along the cirrus to the arm-sinus, constitutes 

 the cirrial muscles (m. cr.). Sometimes a septum is seen in the 

 cirrial canal, spanning the space between the inner or muscular, 

 and the outer or non-muscular side (PI. VIL, Fig. 121). In the 

 canal blood corpuscles are found. 



Between the epistome and the mouth there occurs a recess 



