THE HEART OF THE ANTARCTIC 



Cape Roy ds, twelve kinds of creeping rotifiers were found. 

 Eight of these were well-known kinds which elsewhere 

 lay eggs, and at Cape Royds they are reproduced in the 

 same way. 



There were, however, two other kinds at Cape Royds, 

 unknown anywhere else, and these are greatly more abun- 

 dant than any of the others. It has been told how one of 

 them forms blood-like patches in the lakes. Now, these 

 two species bring forth living young, yet they belong to 

 groups which usually lay eggs. One of them belongs to 

 a genius (adineta), no other known member of which is 

 viviparous; the other {philodina gregaria) belongs to a 

 section of the genus in which all the previously known 

 species are oviparous. 



It is obvious that this mode of reproduction, being 

 unusual in the groups to which they belong, must have 

 been developed as an adaptation to the peculiar conditions, 

 and their extraordinary abundance shows that it is per- 

 fectly successful. Yet this is contrary to our preconcep- 

 tion of what will be favourable under severe conditions. 

 It is usually supposed that eggs are better protected 

 against evil conditions than the adult animals, and that 

 production of winter eggs ensures the continuation of 

 the race when the animals perish, and it appears to be 

 generally so among the lower invertebrata. Yet here, in 

 one of the severest climates in the world, the process is 

 reversed. Not only are the animals viviparous, but parents 

 and young are alike indiff erent to prolonged interruption 

 of their activity by freezing, and when thawing occurs, 

 development proceeds from where it left off. Since the 

 viviparous rotifers are the most successful in the struggle 

 for existence at Cape Royds, it is rather curious to note 

 the total absence of animals of the genus Rotifer, which 

 are all normally viviparous. 



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