426 MEMOIRS OP THE NATIONAL ACADEMY OF SCIENCES. 



nodules in its meshes, begin to show retrogressive tendencies. They sometimes appear swollen out 

 to an unusual size, and their chromatin is aggregated into a single large ball, which may become 

 vesicular and strongly refractive. The cliromatin ball is sometiraes of large size, central in posi- 

 tion, and stain6<l intensely, suggesting strongly the nucleus of a blood cell, or it may stain so 

 faintly as to be hardly recognizable. Again, it may be eccentric and attended by one or more 

 smaller balls, or the nuclear body may be filled with numerous coarse grains. These bodies then 

 recall yeast cells in process of producing ascospores. As in the yeast cell, the wall of the 

 nuclear body seems in many cases to break down and thus set free into the yolk the naked, spore- 

 like masses of degenerating chromatin. 



In Figs. 21 and 32 (Pis. xxvii,xxix), taken from the egg-nauplius embryo, we see various stages 

 of this process. Around the stomodajuni, and within or near the pockets of the antenuie and mandi- 

 bles, there are large numbers of these pseudo-spores. Some are small chromatin balls (s), which 

 combine actively with hcemotoxylon, while others stain feebly or are quite unaffected by the dye, 

 and resemble straw-colored particles of vesiculated and altered food yolk. Below and to either 

 side of the stomod;eum there is a granular residue (Fig. 118, A. Y. S.), composed of yolk and nuclear 

 matter in various stages of chemical degeneration. 



The ordinary nucleus in the resting condition is generally characterized by the presence of 

 balls, nodules, or granules of various sizes, which represent chromatin constituents of the nucleus. 

 Under high powers these usually appear as stellate masses suspended in the nuclear reticulum. 

 A number of representative nuclei are shown in Fig. IS. They are all drawn to scale and are 

 taken from the egg nauplius series under review. It is so plain that it is hardly necessarj- to state 

 it, that the nuclear fragments in these bodies, e,/, or h for instance, correspond to similar fragments 

 which occur free in the yolk. The larger nodule in the nucleus / resembles figure b, except that 

 the latter is surrounded by an outer light zone. This zone is often very large and not as sharply 

 defined as in the drawing. Again, figure c resembles figure h, except that the outer light zone is 

 larger in c and the chromatin or stainable residue has nearly disappeared. I regard the bodies b 

 and c as masses of degenerating chromatin which have escaped from a disrupted nucleus or cell. 

 In c the retrogressive changes are furthest advanced. Finally, when the chromatin or stainalile 

 matter has been completely disorganized, there is left a vesiculated mass which stains very feebly 

 or not at all, and resembles yolk (Figs. 102, 107, A. Y. S.). Nearly every drawing of the egg- 

 nauplius stage shows one or more bodies resembling b in Fig. 18 (see Fig. 21,s, s^, and Fig. 32, s'). 

 In many cases the outer light zone is cloudy, as already stated, and the element resembles a spherule 

 of yolk with a ball of chromatin imprisoned in it. These bodies bear a certain resemblance to 

 blood cells, but this resemblance is probably transitory, and after a careful studj' of a great many 

 stages I can find no direct evidence that they are ever reorganized into new tissue. The blood 

 cell of the adult is shown in Fig. 19 and that of an embryo in Fig. 35. In each case it consists of 

 a deeply staining granular nucleus and a clear cell body. The nucleus corresponds to the 

 apparently naked yolk nucleus (Fig. 35, Mes.; Fig. 18, etc.) and the cell body to the perinuclear 

 jyrotoplasm, which is present, though often of small quantity, in the wandering cells. As we have 

 already shown, it is probable that the blood cell (Fig. 35, B. C.) is derived directly from the wan- 

 dering cell (Mes.), and that the characteristic appearance of the cell protoplasm is a rapid acquisi- 

 tion. 



Degenerating nuclei may be seen by glancing over the plates (Pis. xxxvri-xxxixand xli-xliv), 

 but it is unnecessary to refer to these in detail. 



The dorsal plate or dorsal organ (?) furnishes a most striking instance of the degeneration of 

 cells (PI. XXIX, Fig. 36; PI. xlvi. Fig. 153). Its cells seem to originate from the ectoblast, with 

 a<!cessions possibly from the wandering cells. After the slight ingrowth, which takes place in the 

 middle of the plate, many of the cells pass into the depths of the egg and break up into meteoric 

 clouds of small deeply staining particles. 



To sum up the previous remarks which relate to the appearance of these bodies in Alpheus, 

 degenerating cells are first seen in Stage iv, and in the following egg-nauplius stage they are 

 abnndaTit. In Stage Vli (PI. XLIV, Fig. 131) they are still present, and in Stage viil there is a 

 fresh irruption of degenerating products into the yolk, arising from the centripetal cells of the 

 ilorsal plate. At a slightly later period they have almost wholly disappeared. Even as late as 

 in the tenth stage a few chromatin granules can be seen iu the region of the dorsal plate. 



