20 SYNOPTIC COLLECTION. 



cases they bear, at some time of life and especially when 

 young, indubitable proofs of their evolutionary history. 

 These proofs or revelations of their past condition make 

 the reduced forms more complicated in reality than at 

 first appears, and it is these structural characters which 

 should receive a clear descriptive term free from ambig- 

 uity, since it is these characters which are of very great 

 importance in tracing the phylogenetic history of animals. 



The habit of fusion which has been observed in Pro- 

 tomyxa is probably one important cause of the origin and 

 differentiation of the organ known as the nucleus. We 

 cannot suppose, however, that this process of differentia- 

 tion was rapid, so that a well developed nucleus was made 

 at once, but there were doubtless transitional organisms in 

 which the nucleus was in the process of forming. We 

 had arrived at this conclusion before having seen the 

 work of Gruber x on Pachymyxa hystrix. 



In this form, Pachymyxa hystrix (PI. 8, figs. 3-7 ; fig. 

 3, a living specimen containing brown food material, and 

 fig. 6, the same probably in the process of division), 

 Gruber was never able to observe a nucleus, but he saw 

 scattered in the protoplasm a large number of dark 

 colored granules which became red when treated with a 

 reagent (PI. 8, fig. 5). Specimens were also seen where 

 the colored granules were surrounded by a colored zone 

 of protoplasm so that they looked like little swarm buds 

 (PI. 8, fig. 4), but the exit of these small bodies was not 

 observed. This form of Pachymyxa has an outer layer 

 differentiated into thickly set rods, between which the 

 pseudopodia are thrust out. This is seen in PI. 8, figs. 

 3-5 and 7; in the last figure, fig. 7, a small portion is 

 magnified, showing the rods and one pseudopodium 

 drawn while in the coloring fluid. 



iZeitschr. f. wiss. Zool., XL, 1884, p. 122. On this subject 

 Gruber says we may suppose that a stage preceded the formation of 

 the typical Rhizopod nucleus, when little grains of nuclear substance 

 lay scattered through the whole protoplasm, and that these only 

 came together later to form the real nucleus. 



