220 
influence upon the structure of the sphincter. The ectoderm of the 
tentacles is high with rather numerous nematocysts. The longitud¬ 
inal muscles of the tentacles and radial muscles of the oral disc 
are ectodermal. Their folds are not or only a little branched and 
palisade-like arranged. The actinopharynx is high and contains 2 kinds 
of nematocysts, partly riblike, partly broader at the basal end, and 
with visible basal part to the spiral thred. The siphonoglyphes are 
distinctly differentiated, their endoderm considerably thickened, in 
other parts of the actinopharynx thin. 
The mesenteries are hexamerously arranged in 4 cycles, of 
which the fourth is incomplete. In no dissected specimen I have 
found more than 44 pairs in all and this in 2 specimens with 88 
tentacles. 3 other specimens had 37, 37 and 38 pairs. Character- 
istic to the development of the mesenteries of the fourth cycle is 
that they always seem first to arise in the exocoels situated next 
to the mesenteries of the second order. In two specimens with 
37 pairs the arrangement was in 5 primary exocoels (1)34243(1), 
in the sixth (1)434243(1). There is thus only a single pair of the 
fourth order developed in the exocoels next to the mesenteries of 
the first order. In the specimen with 38 pairs the arrangement 
was similar except that two pairs of the fourth order were devel¬ 
oped next to the primary mesenteries. In the specimens with 44 
pairs most mesenteries of the fourth cycle were regularly arranged, 
in 4 exocoels bordering the primary mesenteries they were lacking. 
In no case have I seen the mesenteries of the fourth cycle devel¬ 
oped earlier in the outer compartments of each hexamer than in 
the inner. All mesenteries of the three first cycles and at least 
part of those of the fourth are perfect. The longitudinal muscles 
of the mesenteries form well developed broad bandlike pennons. 
These latter show often deep longitudinal furrows (humps on sec- 
tions). The muscle folds are in the strengest mesenteries of the 
longest specimens richly branched and numerous. The parietobas- 
ilar muscles are well developed and form a distinet fold on the 
mesenteries. Where the parietobasilar muscles have grown on the 
main lamella of the mesenteries there are mesogloeal muscles. The 
basilar muscles are well developed. The mesogloea in the region 
of the ciliated tract is provided with numerous cells, especially at 
