Part IT.—Stichodactyline and Zoanthee. 191 
and arranged at a different height in different cells in such a way that in sections 
they give rise to a very characteristic deeply-staming zone. Elsewhere in the 
polyp the association of histological elements is more varied, glandular cells or 
nematocyst-bearing cells mingling with supporting cells. 
In two of the present species of Parazoanthus—P. separatus and P. monostichus 
—little or no reflected ectoderm is developed, and the mesenterial filaments are 
simple throughout, that is, only the middle lobe is present, not the lateral lobes. 
In longitudinal sections the ectoderm of the stomodzum is seen to be in 
continuity with the similarly deeply-staining tissue along the free edge of the 
mesenteries, but this is not continued for any distance up the faces of the latter ; 
while transverse sections through the free edge of the mesenteries never present 
any structure which can be regarded as the Flimmerstreifen. P. tunicans exhibits 
on some of the mesenteries a weakly developed reflected ectoderm, and the 
filaments are trilobed for a very short distance below the termination of the 
stomodeeum (PI. xv., fig. 4). 
In the figure which Haddon and Shackleton (1891, pl. Ix., fig. 6) give of a 
transverse section through the terminal region of the stomodeeum of P. axinelle, 
the reflected ectoderm is strongly displayed, and on the free mesentery the fila- 
ment exhibits the characteristic trifoliate appearance. In the genus Parazoanthus 
then every stage can be obtained in the presence or absence of the typical trifid 
Actinian filament, the variation evidently being dependent in some degree upon 
the dimensions obtained by the polyps. 
The absence of the Flimmerstreifen from the mesenterial filaments is now 
known for several Actiniaria outside the Zoanthez, and is the condition exhibited 
throughout the Madreporaria, as far as these have been studied. The character 
must be regarded as indicative of a lower degree of Actinozoan development, and 
in the two species of Parazoanthus mentioned, may be correlated with the very 
diminutive size of the polyps not necessitating the same vigorous internal circu- 
lation. 
Professor Haddon and Miss Shackleton draw attention to the fact that the 
endoderm is often implicated in the upward reflection of the lower edge of the 
stomodzum. It is very noticeable in Parazoanthus avinellw, the appearance in 
which species they figure. The same condition is also to be observed in all the 
species of Parazoanthus coming under my notice, as well as in many other Actini- 
aria and Madreporaria. In longitudinal sections it is evidenced by a strongly 
marked concave border to the mesentery as it leaves the stomodzeum. 
As the authors referred to remark, it has probably no morphological significance, 
and is no doubt exaggerated in a retracted state of the polyps. 
The members of the genus exhibit a certain relationship in regard to the 
presence or absence of pigment granules and of zooxanthelle. It is usualiy 
2K 2 
