58 LIFE : OUTLINES OF GENERAL BIOLOGY 



larger amount of yolk, in requiring to be fertilised, and in their 

 slower development. They are adaptively protected, not only against 

 cold — for they can survive the freezing of the water — but against 

 drought, and their formation is by no means confined to the winter. 

 It might be better to call them "resting-eggs" (German, Dauer-eier). 



In the Turbellarian Mesostoma there are hard-shelled cross- 

 fertilised "winter-eggs" and thin-shelled summer-eggs, probably 

 self-fertilised within the hermaphrodite parents. The winter-eggs 

 are laid in summer, but remain dormant through the autumn and 

 winter. Some species of Mesostoma form only the hard-shelled ova, 

 and this is true of most of the members of their family — the Rhab- 

 docoel Turhellarians, a fact which may account for their wide geo- 

 graphical distribution, since such well-protected eggs can travel 

 on birds' feet, etc., more safely. 



Reproduction in Rotifers is somewhat complicated ; but we may 

 distinguish {a) the ordinary "summer-eggs" which are unfertilised 

 and develop quickly; {b) in certain conditions, e.g. the approach to 

 a temperature associated with the drying up of the pool , the produc- 

 tion of small, unfertilised eggs which develop into males; and (c) 

 the formation of fertilised "winter-eggs" with hard and often 

 prickly shells. These are particularly adapted to withstand drought, 

 and are best called "resting-eggs". In their development there is an 

 interesting adaptive suppression of a larval phase that is commonly 

 seen in the case of the "summer-eggs". 



A comparison is often made between the lethargic condition of 

 animals and the state of the sown seed in the ground. But it should 

 be noticed that the latent period in seeds is a time of necessary 

 preparation, and may extend over more than one winter. In the com 

 of wheat that "dies" in the ground there are intricate processes that 

 prepare the way for the development of the seedling. Who shall 

 say whether there is in the grain, as Treviranus thought, a dim 

 dreaming of the ear that is to be, but there is no doubt as to the 

 fermentations and cell-divisions that are involved in germination. 

 The "dying" is a being bom, and the seeming inactivity a restlessness. 

 It is plain that this should be compared only to the reawakening 

 phase in the inert snail or in the dormant chrysalis. The dry seeds in 

 the store, alive yet not living, they are what we should compare 

 with those profound winter sleepers in which functionality of every 

 sort is reduced to a minimum. 



OTHER STATES OF VITA MINIMA.— From among the lower 

 orders of animals a good example of the lethargic state, where 

 vitality sinks to a very low ebb, may be found in the Roman snail. 

 Getting under moss or the like in some sheltered place, it makes a 

 smoothly lined hole in the ground, and goes to rest with the mouth 

 of the shell upwards. Retracting the whole of its body, it draws across 



