CLASSIFICATION OF ACTINIARIA 563 
when present, mesogloeal. Acontia are often present. Real 
vesicles or frilled tentacles do not occur (the tentacles are 
slightly complicated in one or two cases), nor do acrorhagi ; 
there is never more than one tentacle to an endocoel (often 
there are more in Endomyaria, and it may be so on the exocoels 
algo), and the tentacles often have a thick basal mesogloeal 
swelling aborally. Thick body-walls and knobs and crests 
of mesogloea are fairly frequent (see Part I, Text-figs. 24, 25, 
26, 27, 31). Tentacular musculature is more often mesogloeal 
than in Endomyaria. 
Possibly the acontia in the second group, the acrorhagi and 
vesicles and complex tentacles in the first, are different expres- 
sions of stinging tendencies along different lines, going with the 
sphincter-difference and so on, the frills especially associated 
with warmer seas, the curiosities of the Mesomyaria often 
connected with deep water. One difference is that acontia 
seem to have been ancestral in the Mesomyaria and to have 
been lost in certain cases ; whereas vesicles and such things 
must be the attainments of certain individual sets of animals 
at given points. 
Lastly, evolution within Endomyaria may be a little more 
closely thought of. lor Mesomyaria see Part I. 
The general direction has been decided on (see p. 554). 
The simplest way will be to put the route suggested by the facts 
as narrative, as before, and it must have been something more 
or less like the following : 
From an Eoactinia (near to Hosagartia—see Part I) 
or Halcampa-like form with little or no base, no sphincter, 
and six pairs of macrocnemes and a few microcnemes, at 
first one line of evolution only started. 
An adherent base was gained, at first, and an increase in 
the number of tentacles and microcnemes, but nothing else 
(cf. Text-figs. 8 and 16, c). There are survivors of this stage 
even now, the Condylanthidae. 
Next, the distinction between macro- and microcnemes was 
lost, but at first only the former macrocnemes remained perfect 
(cf. Text-fig. 16, p). Some forms began to get an endodermal 
