III.] LIFE AND DEATH. 151 



tinction between simple growth and true development accom- 

 panied by changes in form and structure. For instance, 

 Hackel's Protomyxa aurantiaca divides within its cyst into 

 numerous plastids, which might be spoken of as germs. But 

 the changes of form which they undergo before they become 

 young Protomyxae are very small, and for the most part depend 

 upon the expansion of the body, which existed in the capsule 

 as a contracted pear-shaped mass. It is therefore more correct 

 to speak only of the simple growth of the products of the fission 

 of the parent organism, and to look upon these products as 

 3'^oung Protomyxae rather than germs. On the other hand, the 

 young animals which creep out of the germs (the ' spores ') of 

 Gregarina gigatitea, described by E. van Beneden, differ essen- 

 tially from the adult, and pass through a series of develop- 

 mental stages before they assume the characteristic form of 

 a Gregarine. 



This is true development \ But such a method of germ- 

 formation and development are found most frequently, although 

 not exclusively, among the parasitic Monoplastides, and this 

 fact alone serves to indicate their secondary origin. It is a form 

 of ontogenetic development differing from that of the Polyplas- 

 tides in that it does not revert to a phyletically primitive con- 

 dition of the species, but, on the contrary, exhibits stages which 

 first appear in the phyletic development of the specific form. 

 The Psorosperms were only formed after the Gregarines had 

 become estabhshed as a group. The amoeboid organisms 

 which creep out of them are in no way to be regarded as the 

 primitive forms of the Gregarines, even if the latter may have 

 resembled them, but they are coenogenetic forms pjroduced by 

 the necessity for a production of numerous and very minute 

 germs. The necessity for a process of genuine development 

 perhaps depends upon the small amount of material contained 

 in one of these germs, and on other conditions, such as change 



^ True development also takes place in the above-mentioned Ichthy- 

 ophthirius. While in other Infusoria the products of fission exactly 

 resemble the parent, in Ichthyophthirius they have a different form ; the 

 sucking mouth is wanting while provisional clasping cilia are at first 

 present. In this case therefore the word germ may be rightly applied, 

 and Ichthyophthirius affords an interesting example of the phyletic origin 

 of germs among the lower Flagellata and Gregarines. Cf. Fouquet, 

 'Arch. Zool. Experimentale,' Tom. V. p. 159. 1876. 



