Manchester Memoirs, Vol. Lr. ( 1 9 1 6). 5 



The case of radially symmetrical forms is also com- 

 parable with certain inanimate objects, I cannot think 

 of any such objects that receive things from all directions 

 as a Sea-anemone receives its food, but many objects that 

 give out things in all directions, which is the same in 

 principal, such as electric light globes, lamp shades, many 

 forms of stoves, etc., are radially symmetrical. Similarly 

 objects that float or drift through the air, as a jelly-fish 

 floats in the water, are radially symmetrical. As an 

 example of this I may mention the old fashioned balloon, 

 which is radially symmetrical in contrast to the dirigible 

 or the aeroplane, which move rapidly by their self con- 

 tained engines, and are bilaterally symmetrical. 



Here again zoologists will be able to point out many 

 exceptions to the general principle I have enunciated. 

 There is the case of many of the Echinoderms for example 

 which show a very pronounced radial symmetry, but freely 

 move about from place to place. But the Echinoderms 

 have certainly a record in their family history of a pre- 

 vious sedentary habit, and their movements cannot at the 

 best be described as rapid. Moreover, in those forms such 

 as the Holothurians, which exhibit a strong development 

 of muscle bands in the body wall, there is a pronounced 

 tendency to assume a secondary bilateral symmetry. 



The cases of sedentary animals that are bilaterally 

 symmetrical already referred to, such as the Cirripedes 

 and Folyzoa, might be compared to the old railway 

 carriage which has settled down in a field as a cricket 

 pavilion but still retains its bilateral symmetry. 



In comparing animals that are bilaterally symmetrical 

 with those that are radially symmetrical the zoologist 

 observes that there is usually far more variation in the 

 important organs of the latter than in the former. In 

 Hydra for example the only important organs are the 



