221 



On the Relation of Sph^erosira volvox to Volvox 



globator. 



By W. H. Gilburt. 



{Read October 27th, 1876.) 



Plate XX. 



The relationship of many of the lower forms of minute life, both 

 among plants and animals, is a fact which year by year is becoming 

 more and more apparent, so that many which were once considered 

 good species are now regarded as but stages in the life-history of 

 other and more or less different forms. 



Such, without doubt, proves to be the case with the two 

 organisms, the names of which head this paper. 



It appears that Ehrenberg was the first to observe Sphcerosira 

 volvox, and by him it was classed as a distinct species from the 

 better known Volvox glob a tor. As such it was regarded till 1852, 

 when Mr. Busk cast some doubt upon it, and suggested that it was 

 but a stage in the development of the commoner form, his reason 

 being that in water containing Volvox globator no Sphcerosira was 

 at first to be found ; yet after a few days they were there in abun- 

 dance. He likewise carefully examined and described the doubtful 

 species, but of the connection of the two forms nothing further 

 appears to have been ascertained up to the present. 



Fortunately we are now able to carry our knowledge one step 

 further at least, and to show that what has hitherto rested upon 

 supposition was really in accordance with fact. 



On Saturday, the 21st inst., I obtained some water from a pond 

 in Epping Forest, near Walthamstow, containing Volvox globator 

 in great numbers. On first looking at them, nothing particular was 

 observed, save that many were decaying, and were occupied by one 

 or more rotifers and their eggs. Making a more careful examina- 

 tion, I found that in some of the vigorous and more active ones, a 

 difference between the macro-gonidia existed — some of them being 

 smaller in size, lighter in colour, and the disposition of their gonidia 

 less regular (Fig. la). Using a higher power, the difference 



