May IS. 191S Wilt of Gipsy-Moth Caterpillars 113 



difficult to see in fresh preparations; but, if a little acetic acid is added or 

 if the corpuscles are properly fixed and stained, it can be very easily 

 demonstrated. 



To the second type of corpuscle belong curious corpuscles filled with 

 thick colorless globules (PI. XIV, fig. 3, 4). This type is not so plen- 

 tiful as the amoeboid, but one often finds two or three of them to a single 

 field. They are nearly always spherical and never emit pseudopodia. 

 At first the writer confused these corpuscles with the pathological forms, 

 for the colorless globules within resemble polyhedra very much at times. 

 They are perfectly normal appearances, however, and are similar to the 

 "mulberry corpuscles" of Forbes (5) and to the corpuscles described by 

 Cuenot in 1891 (2). Cuenot says, in his work on the grass egger (Gas- 

 tropacha trifolii) that the globules within the "mulberry corpuscles" color 

 yellow with iodin and present all the various albumin reactions. He 

 further states that they are reserve amoebocytes and that various tran- 

 sitional stages between them and the ordinary amoebocytes, in which the 

 albumin (protein) globules accumulate gradually, can be detected. The 

 "mulberry corpuscles" likewise possess a nucleus, which is surrounded 

 by the protein bodies. This nucleus can be very easily seen by crushing 

 the corpuscle (PI. XIV, fig. 5). 



When a gipsy-moth caterpillar becomes infected with wilt, polyhe- 

 dral bodies begin to form within the nuclei of the amoebocytes in a 

 manner very similar to their method of formation within the nuclei 

 of the tissue cells previously described. When the polyhedra originate 

 within the nuclei of the blood corpuscles, they have the appearance 

 shown in Plate XIV, figure 6. The same dancing granules referred to 

 as occurring in the nuclei of tissue cells prior to the appearance of fully 

 formed polyhedra were also noted within the nuclei of many corpuscles. 

 In diseased caterpillars many corpuscles are encountered which have only 

 one polyhedron, or several, within them (PI. XIV, figs. 7-9). Such 

 individual or widely separated polyhedra were not formed within the 

 nuclei of the blood cells, but were probably phagocytized by them on 

 escaping into the hsemolymph through rupture of certain tissue nuclei. 

 Another pathological form of corpuscle encountered very often is that 

 shown in Plate XIV, figure 10. Here the enrire cytoplasm of the cell 

 seems to have disappeared, having been used, perhaps, as nutriment by 

 the virus, and all that remains is the cellular membrane and a nucleus 

 containing several polyhedra. The writer is certain that this is a patho- 

 logical condition of the corpuscles, for these cytoplasmic-free elements 

 were never found in normal animals. 



As the disease progresses, more and more corpuscles become filled with 

 polyhedra, and the number of polyhedra floating freely in the plasma 

 increases appreciably. As stated above, these bodies escape into the 

 blood through the disintegration of tissue nuclei, so that a large number 

 of polyhedra in the plasma is a good indication of the final stage of the 

 disease within the tissues. 



