STRUCTURE AND LIFE-HISTORY OF VOL VOX GLOBATOR. 211 



iuto view where it had been previously impossible to detect them, and 

 as they may be sometimes discerned for an instant when the eye ia 

 applied fresh and unfatigued to the microscope, where even a moment 

 later they seem to be absent, it may be assumed that the structure is 

 universal, though often far too subtle to be detected. It is needless 

 to say that no skill of the draughtsman can even suggest its infinite 

 delicacy, while the figures given in books, not excepting the beautiful 

 drawings in Ehrenberg's " Infusionsthierchen," exaggerate the strength 

 of the connecting lines to the extent cf grossly caricaturing the extreme 

 fineness of Nature's own handiwork. As I sit writing to-day, the 

 afternoon sun of an exceptionally bright day, shining full on my 

 study window, reveals the presence on the outside of the panes of a few 

 spiders' webs, so fine that it is only as the breeze causes them to sway 

 gently to and fro that they shimmer into visibility. When I rise from 

 my seat, and try to discover where they cross the window, they are 

 absolutely gone from my sight. If you will picture to yourself a tiny 

 green bead, surrounded by six others, and disposed upon the outside of 

 this same window, and each connected with its neighbours by one of 

 these fine spider-threads, I do not think the combination will give an 

 exaggerated idea of the superlative delicacy of the network of 

 "protoplasmic threads" with which the surf ace of a Volvox sphere is 

 diapered. 



To return to the gonidia and their history. 



A certain number of these in each individual are selected to 

 produce a group of young Volvoces within the parent sphere. The 

 books fix this number as usually four or eight ; but out of twenty-five 

 individuals now in the field of my microscope, I find only three con- 

 taining four incipient spheres of the second generation, while only one 

 contains eight, and there are four containing five, six with six, ten with 

 seven, and one with nine such progeny. Almost every Volvox, when 

 first discharged from the parent sac, and possessing a diameter of 

 about 1-170", already contains a certain number of enlarged gonidia, 

 destined in due time to become its own progeny. Not only so, but long 

 before its discharge, and while yet it exists as a daughter-cell within the 

 protecting cavity of the parent generation, these selected gonidia are 

 already visible as spots larger and darker than their fellows. (Plate VII. > 

 Fig. 6.) 



The history of these selected gonidia, as it may be traced in a 

 daughter-sphere recently cast forth to seek its fortunes in the world of 

 waters around it, is as follows : — The enlarged gonidium is at first a flat 

 thin circular disk, appressed to the internal surface of the sphere, and 

 being surrounded by eight of the ordinary zoospores, is derived from 

 the coalescence of the two central ones out of a group of ten. (Plate VII., 

 Fig. ia a\) Shortly, this disk assumes a more distinctly oval form, with 

 a slight constriction across its lesser diameter, in which stage it often 

 much resembles a young Cosmarium. (Plate VII., Fig. 46 b'.) It is soon 

 seen to be clearly sub-divided into four, and its thickness having grown 



