237 
mesenteries are fertile, as my specimens, as well as those examined 
by Stephenson, were not sexually ripe. On account of a special 
structure of the mesenteries outside the filaments I believe that 
these mesenteries later on become reproductive organs. According 
to my observations on Bartholomea annulata (3 specimens exam¬ 
ined), werneri (1 spec. examined), Aiptasia tagetes (2 spec. exam¬ 
ined), mutabilis, saxicola and diaphana, and Heteractis lucida (1 
spec. of each species examined), the mesenteries of the first cycle 
are fertile. So it is also with Carlgreniella. (Watzl’s statement of 
sterile mesenteries of the first order is false, he has not examined 
the lower part of the body). Thus it seems clear to me that the 
genera are perfectly homogeneous concerning the distribution of the 
reproductive organs. As regards the size of the mesenteries of the 
first cycle, it ought to be remarked that the fifth and sixth couples 
are often more weakly developed than the other mesenteries of 
this cycle. I have observed this in B. annulata, A. tagetes and 
saxicola. 
Also in a third character the species examined by myself show 
agreement. Stephenson (1920) has observed that A. couchii, 
the type of Aiptasia, is provided with an ectodermal longitudinal 
muscle layer in the uppermost part of the column. I can confirm his 
observations. But not on\y A. couchii, also all the species {mutabilis?) 
mentioned above are according to my examinations furnished with 
such a layer, weaker in some species, somewhat stronger in others. 
The muscles do not seem to form a continuous muscle lamella as 
for inst. in Protanthea and Boloceroides, but the muscle fibrils seem 
more isolated. The muscle layer also ends rather soon, the greater 
part of the column lacks an eciodermal musculature. Also the ne- 
matocysts of the acontia show good agreement in all species. 
I give here at last a diagnosis of the family Aiptasiidae. 
Thenaria with a very weak, elongated mesogloeal sphincter 
(sometimes in young specimens almost endodermal?). Uppermost 
part of the column with weak ectodermal longitudinal muscles. 
Tentacles not retractile. Longitudinal muscles of tentacles and radial 
muscles of oral disc ectodermal. Mesenteries not divided in macro- 
and microcnemes. Fifth and sixth couples often weaker than the 
other mesenteries of the first order. Muscle pennons diffuse. Repro- 
ductive organs from the mesenteries of the first order. Acontia and 
their nematocysts well developed. 
