POLYGASTRIA. 



23 



Nassula. 



than they dart off in opposite directions, and rapidly acquire the normal 

 size and figure. In the Vorticella and some other species, we have 



examples of spontaneous 

 division in the longitu- 

 dinal direction, which 

 commences at the mouth, 

 and extends to the irri- 

 table and contractile 

 stem, from which one or 

 both of the new formed 

 individuals detach them- 

 selves. In some species 

 this spontaneous fission, 

 which corresponds, as I stated in my Lectures on Generation in refer- 

 ence to the ova of the Medusa, in so interesting a manner with the 

 earliest phenomenon in the development of the ovum in the higher 

 animals, is arrested before its completion, but the partially separated 

 individuals continue in organic connection and form compound ani- 

 mals, sometimes in the form of long chains, sometimes branched, 

 sometimes expanding to form a spherical bag, as in the well-known 

 Volvox globator, which was long deemed a single individual of a 

 peculiar species. New spherical groups of Volvoces are throw^n off 

 into the interior of the parent monadiary, 

 which is rent open to allow them to escape, 

 as in^^, 12. 



Another mode of generation is by gemma- 

 tion or the development of buds, which in 

 some species, as Cheromcij grow out of the 

 fore part of the body, and in others, as 

 Vorticella, from the hind part, near the stem, 

 or from the stem itself, from which the young 

 animal soon detaches itself. In most Vorticellidce, as in Carche- 

 sium and Episiylis, the small liberated end of 

 the body opposite the mouth is provided v. ith 

 a circle of vibratile cilia, so long as the in- 

 dividual swims freely : but these disappear 

 when the pedicle is developed. 



With regard to the more common fissi- 

 ^^^ parous mode, Ehrenberg has figured grada- 

 jV tiO'is of this spontaneous division of the or- 

 ganised contents of the integument in the 

 Gonhon (fig. 13.) and Chlamydomonas, 

 which may be compared with the earliest 

 c 4 



Volvox. 



^^ ^^ 



