Ixii THE BEGINNINGS OF LIFE. 



colourless boards; again, sometimes the cells are three or 

 four times longer than broad.' Much variation occurs also 

 in the width of the whole thread in specimens taken from 

 various localities. Having thoroughly ascertained, therefore, 

 the extent of variation which may undoubtedly occur in Lyng- 

 bya, Dr. Hicks seems fully justified when he comes to the 

 conclusion that characters of this kind are utterly worthless 

 upon which to found the distinction of species. And yet it 

 is upon such characters only that the so-called species of the 

 genus Oscillatoria are separated from one another. 



But, it may well be asked, what is the most perfect form 

 of this developmental cycle, in which are included the Algae 

 known as Lyngbya, Schizogonium, Prasiola, and Protococcus ? 

 There is no sexual stage of reproduction to be met with in 

 either of them — one can scarcely be said to be higher than 

 another — they are in fact, as it appears, distinct modes of ex- 

 istence, which may be taken on under the influence of suit- 

 able condition by one and the same living matter. But can 

 we stop even here ? may not these forms themselves be but 

 sub-cycles of a still larger cycle ? The gonidia of Lichens, 

 as we have seen, undergo a process of segmentation almost 

 absolutely similar to that undergone by the gonidial cells of 

 Lyngbya ; we may well ask, therefore. Is it possible that the 

 products of the segmentation of the gonidia of certain Lichens 

 may occasionally assume the Lyngbya mode of growth .? 

 Each form has of course a tendency to reproduce or con- 

 tinue the mode of growth of the form from which it has been 

 immediately derived ; it may therefore continue in almost 

 any one of these stages either for a very long or a very 

 short time, such tendency being extremely weak and not 

 to be compared with that which exists in higher organ- 

 isms, in which the influence of the ' law of heredity' has been 

 gradually built up by the production of similar forms through 

 successive generations. Here the present mode of growth 



