582 Annals of the South African Museum. 



the beginning of inversion resembles the infolding of the blastula, the 

 resemblance is but a temporary one, and the final result entirely 

 different. 



The use of the term invagination in this connection, then, is to be 

 avoided. Kuschakewitsch describes the process as one of " pseudo- 

 gastrulation," but that, too, is apt to give rise to misconception. 

 Janet makes use of the term " Extroversion," and Zimmermann 

 uses ' Inkurvation " for the first half, " Exkurvation >: for the 

 second half of the process. But as the existing English word " Inver- 

 sion " has already been used and, while non-committal, describes the 

 process sufficiently accurately, it seems unnecessary to coin a new 

 word. 



Development of Daughter Colony after Inversion. 



After inversion is completed the daughter colony, still enclosed 

 in its vesicle, remains within the parent rotating on its axis, which 

 itself is constantly altering its position. If the reproductive cells 

 have not become apparent before inversion, they are very soon 

 clearly distinguishable in the embryo colony (Plate XXXIX, B). 

 The daughter increases in size, both somatic and reproductive cells 

 becoming larger, and the cilia lengthening proportionately. 



Shaw (1922a, p. 491), who had certainly never seen living material 

 of F. Rousseletii, thought that in this species the gonidia were not 

 differentiated in size until some considerable time after birth, but 

 he is mistaken in this ; they are quite distinct very soon after inver- 

 sion, long before the colony escapes, though they do not divide until 

 later. 



Zimmermann (1925, p. 401) states that in F. globator the size 

 increases rapidly by separation of the cells due to continuous swelling 

 of the intercellular substance, " so that sooner or later the daughter 

 colony squeezes itself into the interior of the mother colony." 

 However that may be in the European species, it is certainly not 

 the case in healthy colonies of either F. Rousseletii or F. capensis, 

 unless very exceptionally. However large or numerous the daughter 

 colonies may be, each remains enclosed in the vesicle formed from 

 the gonidium wall, which enlarges with the developing colony and 

 remains intact right up to the birth of the latter. It is large enough 

 to allow ample room for the daughter to move freely within it. 



