606 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
connection with the surface, and is everywhere separated from the 
ectoderm by an intermediate layer of mesenchym. Although the 
author made a careful search be was unable to find at any stage any 
indications of auditory organs. 
The musculature of the body-wall is formed by cells of the parietal 
enterocoel. The first formed is the median ventral longitudinal muscle 
which may, on the ninth day, be made out as a fine simple layer of 
longitudinal fibres on the inner side of the median ventral radial canal. 
The separation of the retractor muscles from the longitudinal is not even 
indicated till the one hundred and eleventh day. 
The ectoderm and mesenchym form in the young Cucumariae a con- 
tinuous tissue which does not till later on become differentiated into a 
distinct epithelium and an underlying layer of connective tissue. The 
blood-vascular system is derived from the remains of the cleavage cavity, 
or from clefts in the mesenchym. A distinct space appears between the 
visceral layer of the enterocoel and the endodermal wall of the mid-gut 
on the thirteenth day ; this partly forms the marginal vessels of the 
intestine, and partly the blood-spaces which are found in the wall of the 
intestine. Lacunar vessels are similarly developed between the parietal 
wall of the enterocoel and the mesenchym of the body-wall. There is a 
vestibule in front of the mouth which is invested by a unilaminate and 
very low epithelium ; this is continuous with the outer covering of the 
tentacles. On the eighth and ninth days the mouth is very narrow and 
cannot take in food. The coiling of the intestinal tract is obvious on the 
ninth day ; on the fifteenth the mid-gut is considerably widened, and on 
the seventeenth diatoms were observed in it. 
Bathybiaster vexillifer.* — Prof. F. Jeffrey Bell gives a description 
of the type of this rare and incompletely known form which has for 
many years since the cruise of the ‘ Porcupine ’ been inaccessible, and a 
comparison is instituted between it and its since described generic 
allies. 
Coelenterata. 
Phylogeny of Actinozoa. t — Prof. J. Playfair M‘Murrich discusses 
various groups of the Actinozoa from the phylogenetic point of view ; 
he points out certain facts which tend to confirm the hypothesis that the 
Actiniaria are descended from ancestors which possessed an arrangement 
of the mesenteries similar to that which is found in existing Edivardsise ; 
explanations are offered of a few points which do not seem to support it. 
It is probable that the Actinozoa are to be traced back to an ancestor 
which possessed only four mesenteries. The Edward sia-stage, in which 
there are eight, is repeated in the ontogeny of the Cerianthese, the 
Zoantheae, and the Hexactiniae. The first of these come off close from 
the Edwardsia stock. The direct line of descent leads to a stage in which 
twelve mesenteries are present ; the four additional are imperfect and are 
arranged in two pairs ; so far as we know, this stage is now only larval, 
but it seems to represent an important epoch in development. 
A second offset from the main line gave rise to the Zoantheae, while 
a third leads to such forms as Scytophorus , in which there is, in addition 
* Proc. Zool. Soc. Loud., 1891, pp. 228-31 (2 pis.), 
t Journal of Morphology, v. (1891) pp. 125-61 (1 pi ). 
