No. 2.] MORPHOLOGY OF THE ACT/NOZOA. 137 



sponding to the similar pair in C. incmbraiiacctis, which von 

 H eider terms the Continuous septa. Between these, and in 

 reality constituting the ventral directives, is a pair, as in C. uiem- 

 branaceus, which are very short, and hardly extend below the 

 level of the lower opening of the stomatodasum. Next to the 

 ventral continuous mesenteries on either side comes a mesentery 

 which only extends a short distance beyond the middle of the 

 column. Dorsal to it come three continuous mesenteries, the 

 middle one of which, however, hardly reaches the extremity of 

 the body. Then follow two extending slightly beyond the mid- 

 dle of the column, and similar in length therefore to the one 

 immediately succeeding the ventral continuous mesenteries : 

 and succeeding these is a single continuous mesentery. So far 

 the symmetry has been perfect, and I have found the arrange- 

 ment here described to hold in another specimen which I studied. 

 Unfortunately, the third specimen I had for investigation was 

 not favorable for the examination of the mesenteries. 



The succeeding mesenteries passing dorsally on either side 

 vary from the regular arrangement. They are more recent in 

 date of formation than those towards the ventral line, and may 

 not yet have reached their final development, or may remain in 

 this somewhat immature condition. On one side, dorsal to the 

 continuous mesentery last mentioned, there is another similar to 

 it, but on the other side occurs one belonging to what may be 

 termed the second grade, reaching only to about the middle of 

 the column. Occupying the dorsal region are four mesenteries, 

 all of the second grade, two alternate ones, however, being 

 slightly longer than the other two. Upon what is the left side 

 of the figure a mesentery, also of the second grade, was detached 

 in making the longitudinal incision, and was omitted from the 

 drawing. The last mesentery of the second grade on the left 

 side is the youngest of those of the first two grades, being near- 

 est the median dorsal line. 



I have denoted the mesenteries so far described according to 

 their length as the first and second grades, the latter being the 

 shorter ones which extend only about half-way down the 

 column. In the figure (Fig. i) these mesenteries are the only 

 ones represented for the most part, but three (3) still smaller 

 than those of the second grade are indicated. In reality, the mes- 

 enteries of this third grade alternate with those of the first and 



