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Mesenteries. I he secondary mesenteries and the sagittal primary ones are only visible 
in the middle part of the polyp. None of the mesenteries show a trace of mesogloeal lamellae. 
The thickness of the mesogloea diminishes from 2 p near the bodywall, to less than 1 p at the 
actinopharyngeal side. The transversal primary mesenteries are 3 p broad near the bodywall 
and also diminish in thickness towards the actinopharynx. They are very much convoluted and 
sinuous. In the lateral third parts of the polyps the free border of these mesenteries is swollen. 
This swelling is relatively inconspicuous in the fertile part of the mesentery but much more 
conspicuous in the part near the interzooidal area; furtheron the swelling diminishes together 
with the width of the mesentery. These mesenteries do not reach as far as the extreme limit of 
the polyp. — The transversal mesenteries can easily be followed in the intervening space 
between the middle and the lateral third parts of the polyps. 
The mesenterial filaments are very uncertain ; probably they are numerous and branched 
to a high degree. 
Reproductive organs. There are only ova to be found, with a very thin mesogloeal 
capsule (2 p thick) in the transversal primary mesenteries. The diameter of the ovum is 
105 p; the nucleus is large. Several ova are to be seen in one and the same section. The 
ova occur only in the lateral third parts of the polyps, but not in the middle third part. The 
gastral cavity is large enough to contain them, so that they do not enter the lumen of the 
tentacles. Their mode of origin, or a unilateral situation in the mesenteries, is not to be made out. 
There are no parasites to be seen. 
13. Euantipathes dichotoma (Pall.) emend. 
I will describe the anatomy of a specimen from station 204 as a type and I let it 
follow by the divergations shown by specimens of other stations. I was able to make sections 
through the polyps from stations 64, 79 a , 164, 193, 204, 213, 250 (3 colonies), 257 and 313. 
Tentacles. The ectoderm is composed of papillae, so that the greatest thickness is 
35 p, while it is only 10 p between two papillae. On the top of the papillae there is a 
nematocyst-battery, surrounded by deeply staining glandcells. The papillae are constricted at 
their base. The nervous layer lies very near the mesogloea. There are no ectodermal muscle- 
fibres. — The mesogloea is a homogeneous layer, 15 p thick at the base of the tentacles, 
8 p at their top. Cells are absent. — The entoderm, 20 p thick, has only a very few 
deeply staining glandcells but a great number of hyaline ones. There are no musclefibres. 
Bodywall. The ectoderm, 12 p thick, has the same structure as the tentacular ecto¬ 
derm minus the nematocyst-batteries. There are however a greater number of deeply staining 
glandcells, but only locally; i. a. the interzooidal area has locally so many glandcells as to 
form dark palissades. There are also parts of the ectoderm where there are none at all. The 
mesogloea (5 p) and the entoderm (5 p) are the same as in the tentacles. There is no 
interzooidal septum. 
The layers of the oral cone are resp. 16 p, 7 p and 7 p thick. The structure of the 
layers is the same as in the rest of the bodywall. 
SIBOGA-EXPEDITIE XVII. 
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