Volvox in South Africa. 583 



Birth of the Young Colony. 



From a very early stage in the development of the gonidium, as 

 has already been described, the area where the outer gonidium wall 

 is in contact with the surrounding medium forms the floor of a shallow 

 pit, or depression, in the surface of the mother colony, for convenience 

 spoken of as the parent pore (fig. 3 ; Plate XXXVIII, E, G), and 

 this continues to be the case after inversion. 



When the daughter is ready to escape, however, the pit disappears, 

 and instead of being depressed this area of the parent surface begins 

 to protrude. The daughter shows a kind of boring movement, 

 apparently pressing on the parent wall, and the cells round the pore 

 begin to separate. It appears as if the daughter secretes a ferment, 

 which digests the substance forming the walls between the plastids 

 without attacking the latter or their connecting strands. It might 

 perhaps be possible to test the truth of this theory by micro-chemical 

 methods, but as yet no attempt has been made to do so. Whatever 

 the cause, whether simply increased pressure by the daughter or 

 ferment action, the area of and round the parental pore disintegrates, 

 and the daughter squeezes its way out, leaving behind it a large, 

 irregularly circular gap in the parent (Plate XXXIX, C, D). In 

 the figure the partially separated cells show on each side of the outer 

 pole of the escaping daughter, while the second figure shows the 

 daughter free in the water, and in addition two other colonies showing 

 gaps left by escaping daughters. The edges of the gap sometimes 

 fall back into position, but from the mode of its formation it is 

 obvious that, once formed, it can never completely close again. Each 

 daughter makes its own pore of escape in the same way. 



The exceptions to this rule are so rare that it may be regarded as 

 constant. As an instance the following may be quoted the only 

 case of its kind yet observed : On 16th October 1930 a large colony 

 of V. capensis, measuring 1258 x 1344 /JL on the slide and containing 

 8 large mature daughters, was under observation. The smallest 

 daughter measured 286 x 315 JJL, the largest 329 x 358 /j,, hence all 

 were very near in size. The notes made at the time are : " Daughters 

 all moving, some escaping, boring their way outwards ; the cells of 

 the parent separating, some of the protoplasts swimming away. 

 Two, however, did not escape out, but inwards, and swam about 

 inside the parent (the first case observed) for a short time, then 

 escaped. Gonidia large and distinct, but undivided." But this 

 colony was not freshly collected it was brought in from the ditch 



