120 HALF AN HOUR WITH SEA- ANEMONES. 



that the reproductive organs are attached. In the 

 corallines these organs are always external, whilst 

 in the anthozoa they are always internal. This is 

 another of the marked differences separating the 

 two classes. In the sea-anemones the reproduction 

 is truly sexual, and appears on the chamber walls as 

 reddish bands, filled with ova or sperm cells. Not- 

 withstanding this sexual character, the mode of 

 propagation seems to be dioecious; that is, the ova 

 of one individual is better fertilised by the sperm of 

 another than by its own, and vice versa. The 

 embryo, when extruded, are free-swimming, rounded 

 bodies, furnished with the usual ciliary appendages 

 for locomotion. Subsequently they settle down, 

 and the tentacles develop. At first five or six only 

 appear, but soon afterwards these numbers rapidly 

 double themselves. 



We should have stated that in the corallines, and 

 species allied to them, the stomach, or digestive- 

 cavity, is identical with the body-cavity. In other 

 words, there is only one internal cavity. The 

 animal tissues both of that group and of the sea- 

 anemones are nearly identical ; neither has any true 

 circulatory system, or traces of nervous develop- 

 ment. This is very remarkable, especially in the 

 sea-anemones, whose tentacles possess a high degree 

 of sensibility to touch, and even to light. The 

 number of tentacles, in some species, is as great as 

 two hundred ; they generally occur in multiples of 

 five or six, and are situated in two rows, the 



