5 1 8 JOHNSON. [Vol.. VIII. 



" equatorial plate " distinctly, while that on the left is at the 

 "spirem" stage figured by Maupas ('89, PI. IX, Figs. 7-9). 

 The meganucleus, of which only a peripheral section appears in 

 the drawing, was at complete condensation, and in two distinct 

 pieces. I made out 65 micronuclei adherent to the two, but 

 none were found in the spindle stage except the two above- 

 mentioned. It would be of interest to know whether all the 

 micronuclei divide at every fission, and an even allotment of 

 them to each daughter individual takes place. 



A point worthy of note is the time at which micronuclear 

 division takes place in different species of Infusoria, with 

 reference to the phases of the meganucleus. In Stentor it is 

 considerably earlier than in Paramecium, Stylonichia, or 

 Vorticella, where the division of mega- and micronuclei are 

 nearly simultaneous. 



3 . Ontogeny and Pliylogeny. 



The conception that the development of a new Infusorian by 

 the process of fission is an ontogenetic development, compar- 

 able in some respects to the development of a Metazoon, has 

 impressed itself strongly upon me in the study of fission in 

 Stentor. I do not regard the formation of the proximal 

 offspring as homologous with the building-up of a pluricellular 

 animal from the Qg^. It is rather to be compared to the 

 agamic reproduction of Metazoa by strobilation or segmen- 

 tation, as in the Scyphistoma of Acalephs, in the Turbellaria 

 (Microstomum), and in Annelids (Autolytus, Nais, etc.) ; for a 

 somatic portion of the parent is converted by the regeneration 

 of necessary organs into a new being, whereas the development 

 from the Qgg has a single germ-cell as its starting-point. 



Is it possible to discover in the stages of fission a repetition 

 of the leading facts in the phylogeny of the species ">. When 

 we consider how doubtfully and indistinctly phylogenetic 

 history is generally expressed, even in the ontogeny of Meta- 

 zoa, we shall not be surprised to find the evidences of such 

 recapitulatory stages in the evolution of a Protozoon far from 

 decisive. And while in most groups of the Metazoa we have 

 two checks upon our embryological inferences regarding 



