Structure of Magelona. 425 



wedge in the middle linCj and a sliglitly broader region at 

 the sides where it joins the lamellae. The lateral wall has a 

 better marked, and in the preparations a loosely cellular, 

 belt (due to the escape of the bacillary corpuscles), while 

 the ventral is denser and somewhat broader. The nerves 

 liave now come so close together that the neural canal is 

 thrust beneath them. The fibres of the hypoderm slant 

 downward and inward beneath the neural canal on each side 

 in contraction. The cuticle is very thin over the lateral 

 regions, somewhat thicker on the dorsal aspect, and compa- 

 ratively dense over the nerve-area. 



Toward the posterior end this coat forms a very thin layer 

 over the dorsal and ventral longitudinal muscles, widening 

 at the outer edge of each to join the thicker lateral hypoderm 

 in which bacillary cells abound. On each side of the sub- 

 neural canal there is an increase in breadth, but the median 

 dorsal wedge is insignificant. Near the tip of the tail, 

 again, the neural hypoderm is somewhat larger and passes 

 further outward ; that on the lateral regions also stretches 

 further upward and downward, and abounds in large bacillary 

 cells. The neural canal disappears toward the tip of the 

 tail. 



The tapering tail ends in an intermediate rounded portion 

 and two lateral cirri, as in certain other members of the 

 SpiouidcC. Each of the latter processes has a thin covering 

 of cuticle, the rest being hypodermic tissue, the cells or 

 glands being arranged in a somewhat regular manner, espe- 

 cially along the posterior border, where they pass from the 

 cuticle downward and inward. The cells are flask-shaped or 

 fusiform and contain granules and bacilli. The hypoderm 

 of the cirri blends smoothly into the rounded intermediate 

 portion. 



The description of the lateral lamellte (which are two on 

 each side) falls under this head. Each of these (to take, for 

 example, the fourth or fifth behind the ninth bristle-bundles) 

 has a delicate cuticular investment, the interior being- 

 formed by hypodermic tissue. At the base of the lamella 

 is a group of simple bristles (formerly mentioned) which 

 apparently serves to strengthen the pedicle. In certain views 

 a channel appears in the latter, but no fluid has been seen 

 therein, neither is there a vascular coil in the process. 

 During life considerable contractions occur on the concave 

 side, where the striated muscular fibres lying within the 

 curve of the bristles of the process pass from the inferior 

 margin of the upper lamella to the body-wall, and then turn 

 outward to the upper border of the inferior process. 



