No. 2.] DEVELOPMENT OF MANICINA AREOLATA. 219 
VII. OriciIn OF THE FILAMENTS IN THE ADULT. 
After studying the larval development it seems very sure that 
the filaments of the first twelve mesenteries are ectodermal. 
Further, I think the stage with twelve mesenteries holds the 
key to the condition in the adult. In this stage, Fig. 39, etc., 
there are complete (first and second pairs) and incomplete mes- 
enteries (third pair), both provided with ectodermal filaments. 
Both kinds of mesenteries are exactly comparable with the two 
kinds in the adult, and if the incomplete mesenteries of the 
larva are successively supplied with filaments by the reflection 
and upward growth of the ectoderm, it seems probable that the 
incomplete mesenteries of the adult are supplied in the same 
manner. 
The gap between my series of larval stages and the adult is 
partially bridged over by the transverse sections, Figs. 41 and 
42. The young Manicina from which these sections were made 
was one-eighth inch diameter. I found a couple of about the 
same size on a piece of coral rock. In hardening these two 
specimens I was not fortunate, and they were consequently of 
no value for the study of such fine points as the reflection of 
ectoderm. Fig. 41 is through the cesophagus, and disregarding 
the skeleton, shows six pairs of complete and six pairs of in- 
complete mesenteries. The twelve complete mesenteries repre- 
sent the mesenteries present in the larva, now rearranged in 
pairs and with simple muscle plates (only shown in the directive 
mesenteries). The incomplete mesenteries have appeared ac- 
cording to the general law governing the mesenteries above 
twelve. 
Manicina remains a single polyp until it has reached a diam- 
eter of about one-third of an inch. In this condition it has all 
the characters of the adult, except those dependent on asexual 
multiplication. It is, moreover, not sexually mature. Such a 
coral has, disregarding local irregularities, twelve pairs of mes- 
enteries of the first order (complete), twelve of the second order 
(incomplete), and twenty-four pairs of the third order (much 
more incomplete). Fig. 50 gives a median longitudinal section 
of the coral at this age. The polyp was in a state of complete 
contraction, the oral surface or peristome, Py, pulled down, the 
mouth, Mo, widely open, and the tentacles, 7, retracted. The 
