JOHNSON: PARASITES OF BENTHIC AMPHIPODS 



Staining characteristics of nuclei differed depend- 

 ing on the stage. Except for spores, prespores, and 

 some cells in early Type AA infections, nuclei tended 

 to be purple, not blue, with both chromatin and the 

 matrix staining similarly in some cases. When nuclei 

 at these stages were in mitosis, the chromosomes 

 were little, if at all, bluer than chromatin in resting 

 cells, although sometimes chromatin was more deep- 

 ly staining in the dividing cells. Types of chromo- 

 somes that stained with fast green by the Alfert and 

 Geschwind method (indicating presence of basic pro- 

 teins on the chromosomes) would stain blue in H&E 

 preparations. Chromatin and chromosomes that did 

 not stain with fast green in the Alfert and Gesch- 

 wind method would stain purple with H&E. 



A comparison of Types AA and AV, by develop- 

 mental stage, is given in Table 2. Infections con- 

 sisting of few parasites were considered to be the 

 earliest ones and are here designated stage I infec- 

 tions. Stage II infections consisted of more numer- 

 ous and generally larger organisms, and stage III 

 infections consisted of prespores and spores that 

 usually filled the hemocoel. 



Type AA 



Most Type AA infections were in Ampelisca 

 agassizi (Table 1). Type AA chromosomes of all 

 developmental stages were usually thicker than 

 those of Type AV (compare Figures 2 and 4), and 

 the organisms and their nuclei were larger (Table 

 2). Stage I organisms were scattered through the 

 hemocoel, never numerous, and variable in mor- 

 phology and staining characteristics. The one com- 

 mon attribute was scanty and poorly staining cyto- 

 plasm. Chromosomes were usually distinct. The 

 most usual stage I infection consisted of scattered 

 single cells and small plasmodia with nuclei that 

 measured 3 to 4 /urn and had rather distinct chro- 

 mosomes or chromatin clumps that stained a clear 

 blue. Mitotic figures were not frequent, but were 

 more common than in the other stages. A few cells 

 in a late stage I (or very early stage II) infection 

 probably were polyploid. They had many rather 

 long, tangled chromosomes that sometimes formed 

 partially separated groups within the nuclear area. 

 The nuclei of these cells measured more than 7 ptm 

 in the greater dimension. 



Stage II organisms were more numerous and dis- 

 tinguished by having voluminous vacuolate or foamy 

 cytoplasm (Fig. 6). Chromosomes and chromatin 

 clumps were often obscured because the nuclear 

 matrix stained almost as strong a purple as the 

 chromatin. The nuclear matrix did not stain in the 



Feulgen reaction. Plasmodia were uncommon, 

 always small, and sometimes consisted of short 

 chains of joined cells. Mitosis was rarely seen in 

 stage II and stage III, and probably was closely syn- 

 chronized, which would reduce the probability of 

 finding mitotic figures in fixed material. As the 

 spore stage was approached, nuclei became smaller 

 and bluer, and chromatin clumps and chromosomes 

 gained clear outlines, because the matrix no longer 

 stained. 



By the time of spore formation (stage III), organ- 

 isms filled the hemocoel, and infected amphipods in 

 H&E-stained sections could be distinguished with 

 the naked eye because of their overall dark-blue 

 color. Spore nuclei were spherical, and chromosomes 

 were condensed but tightly packed and impossible 

 to count (Fig. 7). In one infection, synchronized 

 nuclear division had apparently just taken place, and 

 daughter cells had not yet separated, so that bi- and 



6 4 



• 



i 







f 



4P 



•I 





Figures 6-7.— Type AA parasites in Ampelisca agassizi. 6: 

 Stage II. Nuclei do not have distinct clumps of chromatin and 

 the cytoplasm is vacuolate. 7: Stage III (spores) (arrowhead). 

 An unidentified fungus was also infecting the amphipod 

 (asterisk). Figures 6-7, x 1500. 



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