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 by 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 Peridinese 

 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, when 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 organisms 

 has been lifted a little, we recognize 

 that the smallest parts of the cell-body 

 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. 



Fig. 131. Peridineae : species of 

 Cemtium. A, from the Gulf of 

 Guinea. B, from the South Equa- 

 torial currents. After Chun. 



