ALCYONIUM. 101 



shape belonging to the categories which specialists call 

 "warted spindles" (PL III., fig. 21), dumb-bells (fig. 22), 

 Ks (fig. 23), and simple crosses. They are formed in cells 

 budded off from the superficial ectoderm, and are only 

 newly formed at the surface. This accounts for the fact 

 that they are always much more crowded at the surface 

 than they are in the more deep-seated parts of the colony, 

 and also for the fact that in the deeper parts the spicules 

 are always of full size. 



(ii.) The canals are seen most clearly near the surface 

 of the colony (Plate I., fig. 3). They have a sinuous course 

 and appear to anastomose freely. They probably serve the 

 purposes of distributing nourishment and of maintaining 

 an equilibrium in the water pressure of the polyp cavities. 



(iii.) The fine lines, which look like capillary tubes, 

 really consist of strings or rows of cells. They have no 

 lumen, and consequently cannot serve the purpose of 

 transmitting the circulating fluids of the body. We have 

 no definite knowledge of their function, but it is probable 

 that they are mainly concerned in the secretion of the 

 mesogloea. 



Anatomy of the Polyps. 



The structure of the anthocodia? can only be satisfac- 

 torily studied when they are fully expanded. When re- 

 tracted the several organs are so tightly compressed that a 

 correct interpretation of their structure is quite impossible. 

 When fully expanded each anthocodia exhibits a ter- 

 minal slit-shaped mouth (PL I., fig. 4) surrounded by a 

 crown of eight tentacles. The tentacles have a row of 

 short papilliform processes on each side, giving them what 

 is called a pinnate form. The shape of the tentacles 

 changes every moment, slowly extending and retracting 

 or bending inwards and outwards as they are stimulated 

 by minute particles floating in the water. In the living 



