60 SYNOPTIC COLLECTION. 



and afterward sucked into the body of the Podophrya by 

 means of the sucking tube, though the process is not well 

 understood. 



Propagation takes place by the formation of buds or 

 embryos from the oral surface. Eight of these buds are 

 seen in PI. 58, fig. 4. The nucleus in the young forms is 

 comparatively simple, but in the large, old specimens it 

 has an extraordinarily complicated structure. This 

 increase in complexity is finely shown in figs. a-e. 

 Fig. a is a young Podophrya with a simple horseshoe 

 nucleus ; in fig. b the nucleus has changed its form, and 

 in fig. c it has become forked. Fig. d shows four embryos 

 with the branches of the nucleus extending towards 

 them, and in fig. e they have penetrated the embryos. 



In this sketch of the Protozoa we have attempted to 

 point out some of the many differentiations whereby a 

 structureless mass of protoplasm, like Protamoeba, may 

 become a specialized organism like an Infusorian. 



MESOZOA. 



The division of animals known as the Mesozoa holds 

 middle ground between the Protozoa and the Metazoa, 

 and is of great importance from a phylogenetic point of 

 view, as will be seen hereafter when the development of 

 the egg of a Metazoan is traced. 



The Mesozoa are represented in the collection by 

 Volvox globator L. No drawing can reproduce the beauty 

 of the living Volvox. A tiny ball of vivid green, it 

 revolves through the water with graceful and rapid mo- 

 tions, offering a puzzle to both the botanist and the 

 zoologist. Although claimed as a plant by a number of 

 botanists, its morphological relations to animal forms and 

 the history of its development lead many zoologists to 

 place it among animals. 



It seems probable that Volvox has arisen from the 



