﻿106 SMITHSONIAN MISCELLANEOUS COLLECTIONS [VOL. 47 



Larvae are extruded from the parent polyp, either singly or in 

 batches, at somewhat different stages of development in different 

 species. They are only two or three millimeters in length and are 

 generally pear-shaped, the swollen extremity being either the oral or 

 aboral pole. The larvae are able to swim around, with the aboral 

 pole foremost, either directly or shortly after they are free, the entire 

 surface being uniformly ciliated. The ectoderm of the oral pole is 

 o-enerallv charged with numbers of zooxanthellse or yellow cells 



Fig. 13. — Diagram showing the order of appearance of all the mesenteries in 

 a polyp having three cycles. The Roman numerals represent the cycle to which 

 the mesenteries belong, and the smaller Arabic numerals indicate the order in 

 which the mesentery appeared within its cycle. The regularity here indicated 

 is constant for the primary and secondary cycles, but departures may be 

 encountered in the third cycle. The sequence represented is that followed by 

 Siderastrea radians, Astrangia solitaria, Phyllangia americana, and Favia 

 fragum. 



which give a dark appearance to this extremity. The occurrence of 

 such symbiotic algae in the ectoderm cells of the larva is somewhat 

 remarkable, considering that they are never found within this layer 

 in the adult polyp. Moreover, as the larva settles, and assumes the 

 polypal form, the algae slowly disappear, remaining in the adult only 

 within the endodermal layer. 



In nearly all coral larvae yet investigated a special development 

 of nervous elements takes place in the ectoderm at the aboral ex- 



