ORDERACTINOIDEA. 31 



ing the single additional function of secreting a Corallum. The 

 preceding cut represents the closed and expanded condition of the 

 Actinia. Their various and gorgeous hues are finely exhibited in the 

 coloured engravings on plates 1 to 5. 



Although these animals are usually attached at bottom, many 

 of them may detach themselves and float through the water to a new 

 resting-place ; or, they will slide along slowly over the rocks, by the 

 action of the base or foot ; and some are said to turn over and walk 

 on the extremities of the tentacles, which affix themselves by a sucker- 

 like action. There is a small group of ActiniaB (Actinectse), which are 

 fitted expressly for an ocean life, by means of an air-cavity in the base, 

 containing a vesicular or spongy disk, made up of air-cells, to serve 

 as a float. The animal lies in the water with its base uppermost, and 

 mouth and tentacles below, and is thus carried about by the winds 

 and currents. 



22. Structure.* The exterior of the Actinia is fleshy, or more or 

 less coriaceous in texture. Though frequently smooth, the lateral 

 surface is sometimes covered with minute warty prominences or 

 tubercles ; occasionally it is furnished with small cup-vesicles, which 

 adhere by suction like the cups of a cuttle-fish, and, by means of 

 them, the animal fixes about it sand and fragments of shells, or aids 

 itself in its progressive motions. The tubercles are sometimes dis- 

 tinctly perforated, and Lesueur and others have seen the water, from 

 within the animal, spurted out through these perforations. Dr. C. 

 Pickering compares the ejections of one seen by him abroad, to a 

 shower from a watering-pot. Whether these perforations are gene- 

 ral in ActiniaB without vesicles, has not hitherto been determined. 

 Evidence of their existence, however, has been distinctly observed 

 in the A. rnarginata of the Boston Harbour, by Dr. Wyman, and 

 this species has not the slightest trace of tubercles ; the skin is 

 fleshy and smooth. They were detected by direct observation with 

 the microscope, after having seen currents of water pass from them 



* Dissections and descriptions of Actiniae have been made and published by Spix, Delle 

 Chiaje, Lesueur, Rathke, Teale, and Quatrefages. In the account here given, the facts 

 have been mostly verified by the author's observations, or by the skilful dissections of Dr. 

 Jeffries Wyman, of Boston. For views of the structure of the spermatic cords, and 

 other interesting particulars respecting the Actinia marginata (Lesueur), of the harbour 

 of Boston, he is indebted to Dr. Wyman's microscopic researches, many of which were 

 made the past summer, during a short residence of the author in that city ; and wherever 

 reference is made above to this species, the observations are those of Dr. Wyman. 



UNIVERSITY 



