794 



MORPHOGENESIS 



mass. This fact is even more striking in virtue of the active part taken 

 by healthy fragments to effect the union. Kepner and Reynolds (1923) 

 reported more than one hundred experiments with several species of 

 Dijjiugia, in which isolated pseudopodial fragments would again enter 

 into the protoplasmic structure of the cell (Fig. 181 ) . Fusion in Dijjlugia 

 is species specific, occurs along the mid-region rather than at the ends 

 of extended pseudopods, and is limited to the fusion between fragments 

 and nucleate cells. The fusion of anucleate fragments with each other 



Figure 181. Reincorporation in Difflugia pyriformis. The small figures show form 

 changes and directional movements of a fragment left by the sudden retraction of a 

 pseudopod (stippled) . The mode of fusion between the fragment and a second pseudopod 

 is shown below. (From Kepner and B. D. Reynolds, 1923.) 



was not observed, even when they were placed in contact. Healthy pieces 

 were reappropriated after separation by distances as great as 1.5 mm.; 

 even those of ectoplasmic composition appeared to move and orient with 

 respect to the parent cell. Autoplastic and homoplastic fusions between 

 individuals of Actinosphaerium ekhornu, under conditions of slight 

 compression, were made by Howland (1928). Permanent fusions were 

 made between two medullary surfaces and between cortical and medul- 

 lary surfaces. Axopodial fragments united with the individual at any 

 point along an unsevered axopodium or with the cortical surface of the 



