246 



I found that in Volvox the third cleavage always procee(is in 

 a dexiotropic manner, and the suggestion lies at hand that here too 

 some peculiarity of the adult form might stand in a certain relation 

 to this phenomenon. What, for example, is the direction in which 

 Volvox rotates round the main axis, is tliis always the same or at 

 one time dexiotropic and at another laeotropic? As has been already 

 observed by earlier investigators and as I can contirm here once 

 more, the rotation always occurs in this way that, seeing it from 

 the animal pole, we may designate it as clockwise, i.e. in the 

 direction of the hands of a clock or dexiotropic. It lies at hand to 

 suggest a relation between these phenomena, as has been stated 

 equally in Gasteropods. That in the latter there can be no (juestion 

 of a direct causal relation between the torsion of the adult animal 

 and that of the cleavage cells will be evident at once if we bear 

 in mind that the spiral cleavage type occurs equally well in forms 

 that are not wound at all, .as Lamellibranchiata, Chitons, Polychaetous 

 Annelids etc. We will revert to the question whether possibly in 

 Volvo.c we might think of a more direct relation between the torsion 

 during cleavage and the direction of the rotation during movement. 



In the eight-celled stage (fig. 4, 5) which has been iigured already 



Fig 4. Stage 8, 

 animal side. 



Fig. 5. Stage 8, 

 vegetative side. 



more than once, the fonr vegetative cells alternate with the four 

 animal cells. They constitute together a little cell-plate representing 

 phylogenetically the Go?iium-s\age, but which at the border already 

 begins to curve in. This curving in accentuates itself during the 

 transition into the 16-celled stage and in Volvox evidently manifests 

 itself somewhat earlier than 'm'Pleodorina, Eudorina, and Pandorina, 

 where also in the stage 16 the cells are still lying in a concave 

 little plate, while in Volvox it has then already passed into a hollow 

 globule with an opening, the "phialoporus". The eggs always have 

 the vegetative side, with the pliialopore, directed to the surface of 

 the maternal organism. 



