226 THE EVOLUTION OF CONTINUITY 



special compressing force would play on the developing 

 organism with inevitable moulding results. It would cause 

 the development of a tapering form like that of a torpedo 

 (Fig. 68). 



It is interesting to note that the form which engineers 

 give to an object, such as a torpedo, so that as it moves 

 through the water friction shall be reduced to a minimum, 

 is the actual form which water-friction forces a plastic body 

 to take when moving through the water. 



But while water-friction could give the elongating 

 primitive Fish (its hereditary symmetrical gifts being re- 

 membered) a tapering symmetrical form with a circular 

 cross-section, it could not unaided mould it on bilaterally 

 symmetrical lines (Fig. 69). 



A- 



Fig. 69. — A, cross-section of Fish ; d, dorsal ; «, ventral aspeot ; 

 d v is the only dividing line which can give symmetrical results. 

 b, cross-section of a torpedo, divisible into symmetrical halves 

 by any diameter. 



While terminal compression of the developing anterior 

 segments of the primitive Fish was going on the anterior 

 mouth was formed (see page 186), the food entering by it 

 passing towards the primitive anus at the opposite end of 

 the organism. This food would be more bulky or coarsely 

 particulate than that enjoyed by the ancestral medusoid, 

 and it would not stream through the alimentary canal, but 

 collect in the stomach to be digested before slowly passing 

 down the intestine. Thus the Fish would, as it were, always 

 carry a load of food material inside it. On the presumption, 

 then, that the digestive contents would be of greater density 

 than the water, their attraction towards the earth would 

 have its influence on the young Fish's physical equilibrium. 

 We are led to this conclusion, moreover, when we examine 



