ORIGIN OF THE SPECIFIC TYPE 



325 



the Peridinese have a definite relation to their power of floating in 

 the sea-water, that the long skeletal arms or horns which these 

 microscopic vegetable organisms extend 

 into the surrounding water form a 

 float- apparatus, for their friction against 

 the particles of the water prevents 

 sinking and enables them to float for 

 a considerable time at approximately 

 the same level. These skeletal forms 

 are thus adaptations, and Chun has 

 recently been able to corroborate the 

 conclusion that this adaptation is exactly 

 regulated, for the length of these horns 

 varies with the specific gravity of the 

 different ocean-currents, species with 

 ' monstrously long ' horns occurring, for 

 instance, in the Gulf of Guinea, which 

 is distinguished b}^ its low salinity 

 and high temperature (Fig. 131, A), 

 while in the equatorial currents with 

 higher salinity and cooler water, and 

 thus a higher specific gravity, there is 

 a predominance of species of Peridineas 

 with 'very short' processes and relatively 

 undeveloped float -apparatus (Fig. 131, 

 B). It could be seen clearly in the 

 course of the voyage that the long- 

 armed Peridinese became more abundant 

 as the ship passed from the North 

 Equatorial current into the Gulf of 

 Guinea, and that by and by they held 

 the field altogether, but later, w^hen the 

 ' Valdivia' entered into the South Equa- 

 torial current, they disappeared ' all at 

 once.' Thus in this case, in which the 

 veil over the relations between form 

 and function in unicellular orsranisms ^ ^^^- ^3i- Peridmeae : species ot 



^ . Ceratium. A, irom the Gulf of 



has been lifted a little, we recognize Guinea. B, from the South Equa- 



that the smallest parts of the cell-body ^''''''^ currents. After Chun. 



obey the laws of adaptation, and consistent thinking must lead us 

 to the conviction that even in the most lowly organisms the whole 

 structure in all its essential features depends upon adaptation. 



