158 



ANIMALS OF LAND AND SEA 



and its progeny do the same, in the course of a single month 

 a thousand miUions would be produced. 



So far as I am aware the rapidity of multiplication of the 

 marine diatoms under optimum conditions has never been 

 satisfactorily determined. But it has been calculated that a 

 single diatom will give rise to a thousand millions in a month. 

 With 6,000,000 diatoms, more or less, to a quart of water in 

 such a locality as Kiel Bay, each one with a reproductive capac- 

 ity of roughly 1,000,000,000 per month, 

 all of the diatoms could be destroyed ex- 

 cept for a single one to each 166 quarts 

 of water, yet in a month the full num- 

 ber would be again restored. This shows 

 clearly the immense advantage the mi- 

 nute diatoms have over larger plants as 

 floating organisms in the sea, and why 

 it is that the marine vegetation except 

 along the shores is all microscopic, 

 and not only microscopic but extremely 

 small. 



The peridinians, coccolithophorids, 

 flagellates, etc., while very different from 

 the diatoms in bodily form and struc- 

 ture, are more or less similar in their 

 relations to the marine world, so that 

 it will not be necessary to consider them in detail. 



While these little plants are able to increase at a most 

 amazing speed and at times occur in incredible abundance, 

 this only takes place under a small range of conditions, occurring 

 for the most part at certain limited seasons. On land in many 

 regions when the drought is broken by the rains grasses and 

 many other plants immediately appear in great abundance. 

 Each grass blade is the equivalent in dry nutritive material 

 of many million diatoms, and the synthesis or formation of 

 nutritive material under these conditions is probably at least as 

 rapid as it ever is at sea. 



Figs. 445-450- 

 Parasitic insects. 



For explanations of the 

 figures see pp. xxiv, xxv. 



