FrcnzeVs Mesozoon Salinclla. 479 



(like, c. (/., Pandorina), but TWO ENTIRE ANIMALS become 

 fused together and form a common cyst. Unfortunately 

 Frenzcl was unable to trace the further phenomena within the 

 cyst. It is, however, hardly possible to imagine anything 

 else than the fusion of each pair of cells of different origin. 

 If, as Frcnzel writes, a continuation of cell-multiplication 

 really takes place within the cyst, this in all probability 

 happens before the copulation of the several cells. Unfor- 

 tunately, too, Frenzel did not directly observe that the sepa- 

 rate similar cells in the cyst pass into the unicellular Ciliatc 

 form which he has described. 



Should that Infusorian really be a developmental stage of 

 Salinclla, it cannot nevertheless, as has already been stated, 

 be termed a larva. The ova of many other animals also are 

 capable of movements, particularly' amoeboid ones, and of 

 feeding in the inthacellular fashion upon the neighbouring 

 cells, such as is the case, among others, in Tuhularia and 

 Hydra ; and not only can this be done by the unfertilized, 

 immature, reproductive cell, but also, as is well known, by 

 the fertilized one, as, for instance, in the case of certain 

 Platyhelminthes, where, in addition to a larger number of 

 yolk-cells, only a few fertilized egg- cells are found in the 

 egg-capsule. The sole difference between SalineUa and the 

 other known cases of active egg-cells is that the latter have 

 only to incorporate and digest the nutritive material which is 

 already stored up for them ; while on the other hand the 

 fertilized ovum (or zygospore) of SalineUa has itself to acquire 

 its food by its own activity, in order to be able to proceed 

 with the building-up of its body. Therefore it is that 

 the faculty of reproducing the organization of the highest 

 unicellular ancestral form in the highest unicellular stage 

 of SalineUa does not, as is the case in the majority of 

 ova, remain virtual and latent. The necessity of accumu- 

 lating the building-material for further development by its 

 own activity only sets in in the case of SalineUa earlier 

 than in that of all other multicellular animals. In point of 

 fact much more is demanded from an independent cell in 

 SalineUa than in higher animals, where the separate cells 

 always retain less of the activity and independent energy of 

 their unicellular ancestors. For the rest, however, the tran- 

 sition from the " cell with intra-cellular digestion to the adult 

 animal with extra-cellular digestion " in the case of SalineUa 

 is by no means more enigmatical and unexplained than the 

 fact that from egg-cells with amoeboid digestion ]\Letazoa 

 develop whose body-cells — partly indeed themselves digest 

 throughout life — for the greater part, however, are endowed 

 with extra- cellular digestion or none at all. 



