24 Edmund B. Wilson 



to consider the radiai Chambers as a trae coelom and their walls as a 

 trae mesoderm homologous with that, for instauce, of AmpJnoxus or 

 Phoronis. 



We ean carry this Suggestion a step farther. With the exception 

 of the anomalous Haimeida (which are very imperfectly known) ali 

 Alcyonaria show a pronounced bilateral symmetry. The cross-sectiou 

 of the body is more or less ovai, the longer axis corresponding with the 

 so-called dorso-ventral piane, and the mouth is greatly elongated in the 

 sanie piane. With respect to this piane ali of the organs are arranged 

 in a bilateral symmetry, which is expressed not only in the adult struc- 

 ture but also in the embryology, as I bave shown in the case of Renula. 

 We can therefore distinguish two terminal unpaired radiai Chambers 

 and a series of paired lateral Chambers. This suggests a direct com- 

 parison between the lateral radial Chambers and the somites of segment- 

 ed animals. Such a comparison may appear at first sight highly im- 

 probable. But if we compare the ideal section of a primitive eight- 

 rayed polyp shown in fig. 16 with the embryo of Feripatus, as figured 

 in Balfour's recent remarkable paper', or with Hatsciiek's figure of 

 the embryo Amphioxus'-^ the comparison loses some of its apparent 

 absurdity. The similari ty between the Peripatus embryo and the polyp 

 is striking. Each has three lateral Chambers (somites of Peripatus) 

 derived in both cases, so far as the evidence shows, as outgrowths from 

 the archenteron. Each has a slit-like primitive mouth, dividcd iuto a 

 well-marked anterior and posterior division''. In Peripatus this primi- 

 tive mouth closes in the middle, the anterior part becoming the embry- 

 onic mouth, the posterior part the embryonic anus. In Alcyonaria 

 it does not dose, but the two pò rtions per si stand per form 

 different functionsduringapart or the whole of the li fé 

 of the organi sm. It is well known that in many Alcyonaria there 

 is a strongly marked ciliated groove, or rather a partly closed tube, on 

 the »ventral« side of the Oesophagus^. This division of the Oesophagus 

 performs the function of drawing water into the stouiach, while the 

 »dorsal« division is concerned with the ino-estiou of food. If these two 



1 Quart Jouru. Micr. Sci., Aprii 1883. Piate XX. fig. 35. 



2 Arb. ci. Zool. Inst. Wien, Bd. IV, Heft I, Taf. IV, Fig. 47. 



3 In the diagnim the mouth has very nearly the aetual form it possesses in 

 Alcyonium and many other Alcyonnria. 



* See, for a brief notice of this structuro a recent paper by Hickson in the 

 Proc. Roy. Soc. No. 220, 1880. 



