14 



engaged. The only observations we possess upon the Em- 

 bryology of these animals, are those of the Norwegian nat- 

 uralist, Rev. M. Sars ; but these concern merely the exter- 

 nal changes which the embryo undergoes. Mr. Desor has 

 devoted a closer attention to the internal organization. The 

 peduncle plays a most important part in the development of 

 the star-fish, being a receptacle for the yolk intended for the 

 nutrition of the embryo ; in consequence of which, its vol- 

 ume diminishes in proportion to the growth of the embryo, 

 until the yolk is completely exhausted, when it is taken up 

 into the body, like a reduced hernia, and becomes part of 

 the intestine. 



After having gone through the Mushroom form, mentioned on 

 a former occasion, the embryo assumes gradually the shape of a 

 pentagon, the angles of which are at first very obtuse, but be- 

 come more and more projecting. After a few days (commonly 

 on the 3d or 4th) a swelling, like a transparent vesicle, may be 

 seen at the lower part of each angle of the pentagon. This is 

 the first indication of the tentacles. Some days after, the num- 

 ber of the vesicles had increased, and there were now for each 

 angle of the pentagon three vesicles, later still five, then seven, 

 &c., being separated by a depression, in which the first trace of 

 the ambulacral furrows was recognized. At the saine time 

 there was a small red dot appearing on each of the terminal 

 vesicles, which proved to be the rudimentary eyes. They are 

 mere pigment cells. On compressing an embryo of this age, we 

 see three separate zones ; an external one, generally somewhat 

 translucent, a second very transparent, and the internal yolk 

 mass, which is most opaque. The same layers exist also in the 

 peduncle. 



On motion of Mr. G. B. Emerson, the thanks of the So- 

 ciety were voted to Dr. Shurtleff, for the great care he has 

 taken, for the time he has given, and for the taste and skill 

 he has exhibited, in providing for the accommodation of the 

 Society and its Collections. 



Dr. William Read was elected a member of the Society. 



