i 3 4 JOHN BEARD [February 



of food-yolk. As compared with the egg of a frog or toad that of 

 a cod-fish contains but little food-yolk, yet the former exhibits unequal 

 but complete cleavage, and the latter partial or meroblastic. Our 

 classification may be convenient for purposes of elementary instruction, 

 but it is purely empirical and has no real scientific basis. 



It is like everything else. With the advance of knowledge, our 

 conceptions of organic Nature become enlarged, and we come more and 

 more to perceive how adverse Nature is to schematic and empirical 

 classifications. But within recent years we have gone further still in 

 the use or abuse of food-yolk in embryological science. It has even 

 been made the basis of a phylogenetic tree of vertebrate ancestry. What 

 more could be asked of it than this ? The discoverer of this tree has 

 indeed disowned and rejected the figment of his own imagination ; 

 but, this notwithstanding, from time to time it tries to blossom forth 

 anew. 



If it could be proved that, as we ascend the vertebrate scale, the 

 food-yolk either increased or decreased in a regular and intelligible 

 fashion, good reason might underlie its use in phylogenetic speculation. 

 But if we attempt to evolve dog-fish and skate from lampreys by 

 increasing the amount of food-yolk in the egg, ganoids from the former 

 by again reducing it, and amphibians from these by a still further 

 reduction, and by a new and enormous increase reptiles from am- 

 phibians, and so on to the end of the mammalian chapter, w r e are not 

 really drawing upon an actual tangible, but limited, supply of food- 

 yolk, but simply and solely on the intangible and unlimited resources 

 of the imagination. 



If it be suspected that the food-yolk of an egg has either increased 

 or decreased, some cause must have been behind the change. It is 

 only in fairy tales, such as that of " Aladdin and the Wonderful Lamp," 

 that things come into existence from nowhere and out of nothing. As 

 in physical science so also in natural science every effect has a 

 cause and every effect is governed by a law or by laws. 



If the food-yolk of an egg can be shown to have increased in 

 amount, we must not forget that the egg has had a history, 1 in past 

 times, and that a plus added to it at or during some epoch of time 

 necessarily entails a minus or abstraction from something else at the 

 same time. 



That this must be so may not be obvious at the first glance. But 

 it is all but certain that the cells in the ovary which feed the ovarian 

 egg (follicle cells), or in other cases the ovarian cells consumed by the 

 ovarian egg, are themselves rudimentary or degenerate or sterile eggs. 

 And the amount of nourishment they can furnish in any given instance 

 would seem to be definite and limited. If the egg of an animal 

 increase in size and amount of food-yolk it may in all probability 



1 This might be termed a " phylogenetic history," were it not liable to be misconstrued 

 into confession of faith in recapitulation. 



