PLATE XX. 



M.FAXDRINA LAF.YRINTH1CA (Ellis & Solander). 



Fig. 138. — Transverse section through the upper part of the polypal tissues covering a coHinal ridge; the column 

 wall and mesenteries on one side belong to a different series of polyps from those on the other 

 side. The irregular parts of the corallum included are the tirst traces of the exsert septa and thecal wall. 



The septa at this level are both entocoelic and ex< lie the Eormer being much hotter developed. 



Certain of the mesenteries are free for some distance at their inner extremity, and others are already 

 attached to the skeletotrophic tissues. The 1 mesenteries are arranged at practically equal distances 

 apart, and no directive pairs occur. The pairs of the two adjacent systems do not correspond. X 75. 



Fig. Kill. —Transverse section through the tentacular region of the same retracted colony. The middle skeletal area 

 represents the thecal wall common to two polypal systems; small exoseptal invaginations occur in 

 addition to the entoseptal. The rounded evaginations of the mesenterial spaces represent the tentacles; 

 the entotentacles [en. t. i are larger than the exotentacles [ex. i. ). • 75. 



Fio. 140.— Section through an incomplete mesentery, and part of the wall of the septal loculus in which it is inclosed. 

 Three ova and two spermari'a occur within the mesentery. The skeletotrophic endoderm is highly 

 vacuolated, the nuclei and protoplasmic contents aggregated mainly toward the margin. 110. 



638 



