HICKS, ON THE DIAMORPHOSIS OF LYNGBYA, ETC. 165 



all events there is nothing in it that would prevent oui' 

 accepting any direct evidence on this point. 



Many of those organisms, whose sexual condition is ap- 

 parently wanting, must be judged of according to the number 

 and kind of stages they are capable of passing throuejh; 

 in other words, according to its whole life-history, rather than 

 by any one portion, however enlarged or apparently compli- 

 cated it may be, or however persistent : for in these lower 

 forms of vegetable life the duration of any one of the stages 

 seems indefinite, and dependent upon outer circumstances. 



In the growth of Lyngbya, here described, there are many 

 points bearing on variation of size, and, indeed, upon the 

 apparent essentials, not only of species, but of genera. 



If we gather specimens from numerous localities, perhaps 

 the first thing that will strike us is the variable condition of 

 the width of the whole thread, as also of the cells individuallv- 

 We shall find these differ remarkably, not only in specimens 

 from different parts, but amongst threads of the same 

 specimen ; and, further, in different portions of the same 

 thread. It is this latter fact which gives complete evidence 

 of the common origin of the different forms. 



The difference between specimens from diflFerent parts is 

 sometimes so uniform, that one might at first sight be in- 

 clined to regard them as difterent species ; yet a little care 

 will seldom fail to supply all the gradations of growth, and 

 in so uninterrupted a chain that there can be no doubt that 

 they are but one form, the different ages of which will easily 

 account for the variation of size. The same remarks will 

 apply to the appearance of the cell-contents. 



Thus, two specimens, taken from different localities in 

 different stages, Avould undoubtedly be ranked as distinct 

 species, if the specific distinctions employed by some algolo- 

 gists were observed. For instance, look at the growing stages 

 of Lyngbya shown in figs. 5 — 8. In some the contents are 

 homogeneous, in some granular, in some nucleated in the 

 centre. These points cannot, therefore, be considered as of 

 any specific value. Again, let any one refer to Kiitzing's and 

 HassaFs genus Oscillatoria. What distinction is there besides 

 that of size, and some slight variations in colour, between 

 their numerous species ? The whole question of size between 

 these so-called species rests upon age, rapidity of growth, or 

 external circumstances. 



The relation of the length of each cell to their width 

 depends merely upon the rapidity of linear segmentation, 

 compared with the individual cell- growth. Thus, that a mass 

 from one locality should vary in size from that from another 



