244 



proportion of chlorophjll, and communicate bj more nnmerons and 

 broader plasmodesms. The cells at the animal pole each contain a 

 red stigma as characteristic of flagellates sensible to light (to which 

 also the Volvocinea belong), whilst those at the vegetative pole are 

 lacking them. The two kinds of cells pass quite gradually into each 

 other. The propagation cells are restricted to the vegetative half. 

 Any one having an opportunity to study Volvox can ensily verify all this. 

 The propagation occurs either by means of egg-cells and sperma- 

 tozoa, or parthenogenetically by so-called parthenogonidia. The latter 

 mode occurs, just as in Rotatoria and Infusoria, during a number 

 of generations, the former mode at the close of such a period, the 

 encysted egg being the result. The cleavage stages of the egg and 

 of the parthenogonidia in which development proceeds in a similar 

 manner, exhibit again a striking resemblance to those of Metazoan 

 eggs. The figures given of these stages for Vo/vo.v, Pleodorina, 

 Eudorina, Fandorina, and Goniuin, remind one especially of stages 

 of the spiral cleavage type, which probably we may designate as 

 the original cleavage type of the Zygoneura or Protostojnia, and 

 which is still found with Polyclads, Nemertines, Polychaetous Anne- 

 lids and most Molluscs. It therefore seemed to me very interesting 

 to find out how far the cleavage of Volvox corresponds to the spii-al 

 type. The statements made b^' former investigators appear to be 

 insufficient and too contradictory to answei- this question in a satis- 

 factory way ^). 



j Fig. 1. Volvox glohutor, parthenogonidium, four-celled 

 stage, seen from the vegetative side. 



When, therefore, the 0[)portunity presented itself to study more 

 closely the cleavage of the parthenogonidia in Fo/yo.i', which appeared 



1) Statements on the cleavage of Volvox are found in: 



J. GoROSHANKiN, 1875, Geiiesis im Typus der palmellenartigen Algen. Versuch 

 einer vergleiclienden Morphologie der Volvocineae. Milt. Kaiserl. Ges. naturf. 

 Freunde in Moskau, Bd. 16 (Russian, an extract is found in Botan. Jahresber. f. 

 1875, p. 27). 



E. Overton, 1889, Beitrag zur Kennlniss der Gattung Volvox. Botan. Gentralbl., 

 Bd. 10, p. 177. 



L. Klein, 1890, Vergleichende Untersuchungen fiber Morphologie und Biologie 

 der Fortpflanzung bei der Galtung Volvox. Ber. naturf. Ges. Freiburg, Bd. 5, p. 15. 



