PLATE XIX. 



MANICINA ARKOLATA Linminis. 



Fig. LSI. — Transvei'se section through the stoniodiieum of a polyp, .showing the relationship of the I'idges and fnrrow.s 

 to the internal attaelinient of the mesenteries. X 110. 



Fic. 132. — Transverse .section through a >-oung polyp toward the inner termination of the stomod;eum. The mesen- 

 terial plan is represented on p. 504, fig. 13/. At this level the edge-zone is already terminated at some 

 places, but persistJ at others. Only certain of the perithecal continuations of the mesenteries extend 

 thus far, and some have ceased their connection with the skeletotrophic wall, while retaining that with 

 the column wall. The isolated portion of the column wall at the upper side of the figure is exception- 

 ally distended, and only fragments of the mesenteries are included. X 70. 



Fiii. l:!3. — Freshly extruded larv;e. In the one viewed from above ( h) tliree pairs of mesenteries are already united 

 with the stomod;eiini, and three other pairs are free. Enlarged. 



Fig. 134. — Another lar\a, about four days old, adherent to a jilate of glass. The mesenteries are at almost the same 

 stage as in the larva represented in fig. 1.33 (h), but pair III, III, has not yet reached the stomodanim. 

 Enlarged. 



Fiii. 13.5. — Young polyji, twenty-one days after extrusion, fixed to glass and viewed as a transparent object. The 

 tentacles are incapable of complete retraction, and appear as twelve s])heroidal knobs arranged in two 

 alternating cycles of six each. The eight Edwardsian mesenteries are complete, but the remaining four 

 are incomplete. The skeleton is represented by six entocadic radiating septa; the basal plate was also 

 developed, but is not shown. X 70. 



Fig. 136. — Another young Jiolyp of the same age, in which the formation of the six septa has not proceeded 

 regularly. The first trace of the columella api)ears in the middle. The tentacles are not distinctly 

 seen, having become depressed in the discal wall. X 70. 



Fig. 137. — Vertical section of tlie young polyp represented in fig. 136, after decalcification. The section passes 

 through the wide oral aperture; the stomod;cum terminates freely on the left side, but is in union with 

 a mesentery on the right side. A tentacular thickening occurs on the left, and serves to delimit the oral 

 disk and column wall. The Ijasal disk is practically devoid f)f any ectodermal (calicoblast) layer, but 

 toward the free column wall at each end it begins to appear. A septal invagination occurs on each side, 

 the polypal wall resting upon them. Histologically the endoderm of the basal disk differs from 

 that of the column an<l oral disk. X 200. 

 636 



