Professor Agassiz's Zoological Researches. 317 



After haA'ing observed that tlie contracted mouth forms a 

 straight Ime, and that the tentacula are placed five by five, 

 so as to form a regular pentagon, one of which is always in 

 the prolongation of this line, the author thence concludes, 

 that there can no longer be any doubt as to the bilaterality of 

 this polypus. 



It is our belief, on the contrary, says M. Duvernoy, that 

 this conclusion can be no longer hazarded ; and we pass on 

 to his observations on the development of the Actinia, which 

 appear to us to be of unquestionable interest. 



" It remains for us to study the mode of formation and the 

 increase in number of the tentacula. The same Actinia 

 which enabled me to observe the symmetry of structure, fur- 

 nished me with the means of doing this. One day I saw it 

 deposit a packet of eggs, which were soon developed, and 

 gave birth to young, provided with ten tentacula only, and of 

 a distinct pentagonal form, which extended to the margin of 

 the interior disc by which they were attached. At this 

 period, the organisation of these animals is very easily under- 

 stood ; the vertical plates which divide the general cavity of 

 the body are ten in number, and the stomach is suspended 

 above this cavity, into which it opens below by a large 

 aperture. A young Actinia, at this stage, i-esembles an Al- 

 cyonium; only in place of eight vertical bands, there are 

 here ten plates, which advance considerably from the inte- 

 rior of the cavity, and which correspond to the ten tentacula 

 of the circumference, or rather which intercept them. These 

 plates are muscular, and, along with the circular fibres of 

 the surface, determine the very varied forms we observe 

 among these animals. The ovaries and the testicles, which 

 are suspended to these plates, are developed at a very early 

 period. The new tentacula are simple prominences on the 

 circumference, which are formed on the outside of the al- 

 ready existing tentacula and between them. The walls of 

 the new tentacula are then prolonged vertically, by project- 

 ing into the interior, and giving birth to new plates. In my 

 new Actinia, the tentacula themselves are plaited on the in- 

 terior, as is the whole animal, and I can distinctly see the 

 fibres, or rather the longitudinal muscular fixscicles which 



