74. NINKTKKNTH KKFUHT. 



separated and went on as before. It is El})aticwsky'.s opinion that the 

 ultimate result of the operation is sporulation of a special type, but the 

 proof is not conclusive. 



One of the common figures of Arcella in texts shows three individuals 

 with the body protoplasm united. This may have some bearing on 

 rei^roduction. but in many cases at least, no nuclear changes are observed, 

 and it is possibly only plasmogamie. The naked protoplasm of the 

 animals is naturally viscous, and when two or more come together they 

 adhere mechanically, without any especial physiological implication. This 

 is very commonly the case with the Heliozoa, in which groups of indi- 

 viduals are often united by a protoplasmic isthmus. It is nevertheless pos- 

 sible that some benefit in the form of rejuvenation follows such proto- 

 plasmic contact. Swarczewsky makes the distinction that conjugation 

 (Chromidiogamie) is a process sugeneris, and can be brought into no 

 necessary relation to plasmogamie. Further observation on tlie phe- 

 nomenon of plasmogamie in tliis and otiier forms is needed before positive 

 conclusions can be drawn. 



Encystment. The occurrence of encystment is common throughout the 

 Rhizopods, as well as the other Protozoa, and in time will probably come 

 to be recognized as an almost universal method of tiding the organism 

 over a period of drought, cold, lack of food, or other unfavorable circum- 

 stances. Other closely related Rhizopods whose cysts have been recorded 

 are Nebela and Euglypha (Prowazec 00). Difflugia (Rhumbler '96) 

 Centropyxis (Scliaudinn 03), Chlamydophrys, Ama?ba, etc. 



With respect to Arcella, cj'^sts of various kinds have rei)eatedly been 

 described. Most of this literature is fragmentary and not easily avail- 

 able. The thesis of Dr. IMartini, (05) prepared under Hertwig, seems 

 to be the most extensive work on the subject. Fifty pages of text with 

 sixty-nine figures deal with the formation, description, and development 

 of the cysts. Many individuals with six nuclei Imd been observed, and 

 the next examination revealed numbers of cysts, as well as many abnormal 

 individuals in the process of encysting. An ei)idemic of cyst-formation 

 resulted in most of the Arcellas in all the cultures passing into this 

 dormant condition. Those that were left multiplied rapidly, and about 

 a month later began a second period of encysting. This agrees with the 

 observations of Hertwig and Lesser ('74 and later), wlio describe many 

 splierical cysts witliin the shells, close to tlie mouth. The first indica- 

 tion of encysting in the 6-nucleate forms was a reorganization of nuclear 

 material, accompanied by an increase in the luunber and size of the 

 vacuoles. At the same time with tlie protoplasmic streaming certain 

 characteristic "soft-bodies" could be discerned. .\fter the disappear- 

 ance of the vacuoles and extrusion of part of llii' c liromatii). the proto- 



