MUSEUM OF COMPARATIVE ZOOLOGY. 143 
It is an interesting fact, tnat even the most thoroughly degenerated 
membranes have numerous nuclei in all stages of division, The divid- 
ing nuclei have undergone the same degenerative alteration as the rest. 
It is impossible to state whether these nuclei had begun to divide after 
the regressive change, or had been overtaken by these changes while 
undergoing division; and it is equally impossible to say whether 
degeneration would have prevented the nuclei from completing their 
division, The division is essentially like that of younger nuclei, but 
often unsymmetrical. 
Not all the degenerative changes are confined to the nuclei. The 
cells also give evidence of modification, Their walls become more 
distinct, not only because they are denser and thicker, but on account 
of their stainability with hematoxylin. The cytoplasm frequently has 
a reticulated structure, which. is densest about the nucleus. In the 
oldest membranes, certain large groups of cells have nuclei surrounded 
by a narrow bright ring, and outside this a much broader halo of a 
radiating structure, which takes a deeper stain than the rest of the 
cytoplasm (see Fig. 34). The appearance of the whole is strikingly 
like that of the “attraction spheres” of ovarian and other cells, but in 
this case has certainly nothing to do with mitosis. If the cell contains 
two nuclei, or a dividing nucleus, each daughter nucleus is surrounded 
by a halo. In early stages of division, however, the elongated nucleus 
has a single halo. I am unable to account for these appearances ; I do 
not regard them as attraction spheres, but rather as a result of degener- 
ation. The attraction sphere should radiate from a centrosome ; here 
it radiates from the nucleus as a centre. I may state, in passing, that 
my search for centrosomes in the serosa has been wholly unsuccessful. 
The pale ring is very generally present around nuclei that have under- 
gone degeneration. It seems to have no intimate connection with the 
radiating zone, being frequently found where the latter is absent. 
The life history of the serosa cells corresponds closely with that of 
certain cells in the Malpighian vessels of Aphrophora spumaria de- 
scribed by Carnoy (’85, p. 219). The cells at the two extremities of 
the tubes contain nuclei not greatly different from those of young 
serosæ, but the nuclei of the middle portion are irregular, jagged, 
and filled with amorphous chromatin. They therefore bear a strong 
resemblance to the degenerated nuclei of the serosa. Furthermore, the 
origin of the peculiar nuclei of the middle portion of the Malpighian 
vessel agrees closely with that of. the degenerated nuclei of an old 
serosa. It is thus described by Carnoy- (p. 220): “Sur les petites 
