No. 2.] DEVELOPMENT OF MANICINA AREOLATA. 227 
with the cells of the mesentery. None of the filaments in these 
young specimens of Cerzanthus ran the whole length of the 
mesentery. Most of them stopped at about the equator of the 
body. 
In the actinias, studied by the Hertwigs, the mesenterial fila- 
ment in the upper part of its course is in section tri-lobed. There 
is a median secretory tract and two lateral ciliated tracts. The 
mesoderm extends into each lobe. On all the mesenteries the 
ciliated tracts are lost in the lower portion of the filament. On 
the incomplete mesenteries the median tract disappears towards 
the upper limit of the mesentery, the lateral ciliated bands 
remaining. On the complete mesenteries the median tract 
merely gets smaller towards the cesophageal end, but does not 
disappear. 
The description I have given of the filaments of Cerianthus 
is, barring slight differences due to age, like the account the 
Hertwigs give for this actinia. From this description it is seen 
that the filament of Cerzanthus corresponds in the main to a 
typical Hertwig filament, such as is on a complete mesentery. 
But the lateral lobes, #, Fig. 47, are very small even in the 
adult when compared with the lateral wings of the Sagartza 
Mament (Fi, Tat. V., Fig. 10). 
The filament of M/anicina is a much simpler structure. It is 
not trifid, though the mesenteric lobes, m./, Fig. 52, give such 
an appearance to the edge of the mesentery. But on referring 
to Hertwig’s figure of Sagartia (Taf. V., Fig. 10), it is evident 
that the mesenterial lobes of Manzcina do not represent the 
ciliated bands of Sagartia. They are totally different histologi- 
cally, and do not contain prolongations of the mesoderm. On 
the other hand, the ventro-lateral tracts of Manzcina do cor- 
respond histologically with the ciliated bands in the Hertwig 
filament, and the glandular lobe of the latter is in general 
similar to the median stripe of the M/anzcina filament. As I 
take it, all three tracts of the Hertwig filament, taken together, 
are homologous with the simple filament of J/anzcina. They 
must all, therefore, be ectodermal: in the young Cerzanthus, 
Fig. 47, the lateral lobes evidently belong to the median lobe, 
and are not modified parts of the mesentery; and since the 
median lobe at a lower level, Fig. 48, shows its independence of 
the mesentery, the conclusion seems to be that the whole fila- 
