390 FUNAFUTI ATOLL. 



The entoderm of the disc is thin and contains zooxanthellrc. 

 The entodermal musculature is weak. 



(Esophagus. The groove (Plate xxvii., fig. 2#r.)is well marked 

 and has in one specimen examined by us, the same truncated 

 form described by McMurrich in G. isolata, and Haddon & 

 Shackleton in G. mutuki. The ectoderm contains large and 

 small nematocysts and a few zooxanthellse are also present. In 

 the basal part of the ectoderm colourless refractive granules as 

 well as groups of yellowish-brown granules are present. The 

 mesoglcea is considerably thickened below the groove. 



Mesenteries. The mesenteries are typically brachycnemic in 

 arrangement (fig. 8), but in one specimen examined the sulcar 

 mesentery of the second pair on one side was perfect, thus realis- 

 ing the macrocnemic condition. The mesogkea of the mesenteries 

 is on the whole thin but is somewhat thicker in the basal part of 

 the column. Peripherally also the mesogloca in each perfect 

 mesentery is thickened where it encloses the basal canal and again 

 becomes constricted before joining the body wall. The imperfect 

 mesenteries are short and bulbous and project little into the 

 ccalenteron (fig. 8). 



Each mesentery encloses a main basal canal appearing in section 

 narrow and elongated in the perfect and rounded in the imperfect 

 mesenteries. In the mesogloea internally to the basal canals in 

 the perfect mesenteries there occur small lacunae. In the basal 

 canals there are present large nematocysts similar to those in the 

 lacunae of the body-wall, and zooxanthellte also occur in the canals 

 and lacunse, but in no great numbers. The basal canals run up 

 into the region of the disc where they divide into several smaller 

 canals. 



The entoderm is a thin layer in which zooxanthellfe are fairly 

 abundant, especially in the O3sophageal region. 



Occasional nematocysts are also present. The parieto-basilar 

 muscles are supported on plaitings of the mesogloea and are well 

 developed. The longitudinal musculature is weak. 



The reflected ectoderm on the two sides of each perfect mesentery 

 give rise to numerous (up to 20) close set ridges of which the 

 inner and outer project freely. Below, the peripheral free portions 

 pass into the mesenterial filaments in the usual fashion. The 

 filaments have at first in section the shape of an arrow-head, but 

 soon the free margins disappear and the central part remains as 

 a bulbous thickening below which the entoderm is also enlarged. 

 Here, just as inZ.funafutiensis, the inner margin of the mesentery 

 has the shape in section of a double bulb. In the ectoderm of 

 the filament there are present occasional zooxanthellae and large 

 nematocysts, while gland cells are very numerous. A few large 



