VOLVOCINES, 59 
greater part of the time it is regularly in the direction indicated, and 
the point of rupture of the sphere will be at its north pole. 
“Tt is difficult to determine precisely how this rapture is accomplished, 
but I believe it to be by a special contraction of the walls of the parent, 
or of the invisible primordial utricle, not by the outward pressure of 
the daughter spheres, this force being evidently inadequate to produce 
the result where their number is small, whatever it may be when it 
reaches its maximum. 
‘“‘ Shortly before the emission of the young the cell commonly assumes a 
slightly pyriform shape, and then slowly opens at its apex, but the aperture 
is of less diameter than that of the young Volvoces, and as each of these 
passes oat, the mouth of the bag is visibly stretched, and resumes its 
original size after each daughter sphere has escaped, so that it evidently 
possesses considerable elasticity, a property also made manifest by the 
fact that the normal form of Volvox may be considerably flattened by 
the pressure of a glass cover, and yet resume both its spherical form and 
its motion when this pressure is removed. : 
“Moreover, the daughter sphere passes out without rotating, and from 
whatever cause it derives its impulse, this often suffices to drive the 
young Volvox clear of the mouth of the sac to a distance equal to 
several times its own diameter, in which position it pauses motionless 
for some seconds, and then, commencing to rotate gently, sails away, at 
first slowly, then more and more rapidly, to enjoy its independent 
existence. 
‘“After the rupture of the sac, the gonidia near the edges of the 
opening are seen to quiver, from the action of the cilia, where they are 
partially freed from the support of the surrounding envelope, and the 
same thing occurs when they are forcibly torn from their attachment, 
in which case they may even move for awhile freely through the 
water. 
“The general action of the cilia continues for some time, and the 
empty sphere rotates as before, its general direction being still from 
north to south, with the open end to the rear. After w time, which I 
cannot specify, the cilia cease to play, and the organism decays, having 
fulfilled its destiny in life. 
“The birth of the young Volvocesis affected by various circumstances. 
Doubtless the process is, under natural conditions, most active in the 
early hours about dawn, when the analogous functions of similar 
organisms are well known to be most energetic, but in order to see the 
phenomenon in fall vigour it is only necessary to place a number of 
mature parent-spheres, such as are found in every colony, in a shallow 
live-trongh, and to bring them into a warm room. In an houw’s time 
almost all the young plants will have been liberated. Light and heat 
stimulate the action, while cold and darkness retard it. The ciliary 
action is affected in a remarkable degree by altered external conditions, 
If a drop of water considerably colder than that in which the Volvoces 
are floating be allowed to flow in under the cover-glass, the whole are 
paralysed for some seconds, after which they slowly resume their motion. 
A sudden mechanical shock produces a similar effect. A sufficient 
degree of heat to make the water distinctly tepid to the feel causes 
instant and simaltaneous death of the whole colony. 
“ During the day the majority of the Volvoces contained in a shallow 
vessel rise to the surface, although they avoid strong direct sunshine, 
while at night they retire in a cloud to the bottom. 
“The astonishing number in which the spheres at times appear in 
some pool, and their equally sudden disappearance, have been frequently 
remarked, Doubtless a very slight change in external conditions suffices 
on the one hand to favour the development of countless thousands of 
