302 FAMILY: MONADIDiE 



Genus : Dimastigamoeba Blochmann, 1894. 



There is some question as to whether the organisms included in this 

 genus shoukl be regarded as Mastigophora or E-hizopoda (Figs. 61, 120, 

 121). It appears that the great part of their existence is spent as amoebae, 

 in damp soil or similar situations, but that at certain times, when excess 

 of fluid is suddenly added to the medium, they temporarily assume a 

 flagellated condition. Two fiagella are developed, the body becomes 

 elongated, and the organism has the characters of a typical member of the 

 Mastigophora. After leading a free-swimming existence for about a day 

 the fiagella are lost, and the amoeboid condition is again assumed. The 

 axonemes of the two fiagella appear to be connected with the nuclear 

 membrane, and in this respect the flagellates resemble those of the genus 

 Heteromita. Division, however, takes place only in the amoeboid phase, 

 during which the nucleus divides in a characteristic manner, differing in 

 this respect from the method of nuclear division of Heteromita. Further- 

 more, the spherical cysts are provided with a number of pores which render 

 them easily recognizable. This genus has been considered more fully in 

 the group of flagellated amoebae (p. 262). 



Genus: Spiromonas Perty, 1852, 



This genus includes flagellates which in the adult condition have narrow 

 elongate bodies which are spirally twisted. There are two fiagella, which 

 arise from the anterior end of the body near a small cytostome. Two 

 blepharoplasts lie near the insertion of the fiagella and the nucleus is 

 centrally placed. When reproduction takes place, the body becomes 

 spherical and enclosed in a cyst, within which division into daughter 

 fiagellates takes j)lace. 



Spiromonas angusta (Dujardin, 1841). — This organism, which in the 

 adult stage has an elongate spiral body 12 to 13 microns long by 1-75 

 to 2 microns broad, was referred to by Dujardin (1841) as Heteromita 

 angusta and Stein (1878) as Bodo gracilis. Kent placed it in the genus 

 Spirofnonas (Fig. 143). It was studied by Woodcock (1916) in cultures 

 made from goat's fseces. The smallest forms have ovoid bodies measuring 

 2-5 by 1 micron, and provided with two backwardly directed fiagella, 

 which may be more than three times the length of the body. As growth 

 takes place the body becomes definitely spiral, while with further develop- 

 ment it becomes bean-shaped. In the largest forms the fiagella are about 

 as long as the body, which undergoes no change in shape and appears to 

 be quite rigid. The nucleus is in the anterior half of the body, while the 

 axonemes of the fiagella arise from two blepharoplasts in front of the 

 nucleus. Multiplication occurs only in the encysted condition, which is 



