MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 427 



CELL DEGENERATION AND AMITOSI8 IN ALPHEUS MINOK. 



Ill the segiuentation of Alpheus minor there are numerous cases which illuHtrate the fragmen- 

 tatiou iiuil apparent degeneration of nnck'i. A nuclear body sometimes seems to be breaking down 

 and discharging a large number of sporelike balls or grains of chromatin (Fijr. 2(i, PI. XXVIII, S. C). 

 This probably represents an clement in i»roco.ss of dissolution, if this be true, the clear area is 

 similar to the plasmalike mass shown in Fig. 13, in which the nuclear bodies have disappeared from 

 view. Clear areas are sometimes seen containing only minute particles of nearly dissolved chro- 

 matin. The large swollen bodies, like those shown in Fig. 23, each with a single, often minute, 

 ball of chromatin, certainly remind us of somewhat analogous structures which can be seen at a 

 later stage in the crayfish. 



The egg sectioned iu Fig. 12, PI. xxvi, contains eight large nuclear nests or shells. The 

 nuclear masses are seen to be very irregular in size, and in some instances the nuclei are unques- 

 tionably breaking down. Iu other cases the egg contains a smaller number of large, very irregular 

 masses of nuclear material, consisting of a fine network, with chromatin granules in suspension. 

 These nuclear masses sometimes appear to be constricting into two parts. The swarm of small 

 nuclei, like that shown in Fig. 13, 1 interpret, as already stated, as arising by a kind of budding of 

 the large nuclear mass and the subsequent constricting ofl" of the buds. 



It is very interesting to find that in this case, possibly the only case of amitotic cell division 

 in the segmentation of the ovum yet recorded, the indirect division of the nuclei is followed to 

 some extent by a degeneration of these bodies. This lends some weight to the view that indirect 

 division is connected with the senescence of nuclei.* 



The nuclei of the large endoderm cells lining the mesenteron in the crayfish appear to divide 

 directly, and in this case the process is again followed by dissolution. In may, however, prove 

 that we have here a case of multiple karyokinesis, similar to that which I have recently observed 

 iu the superficial cells of the lobster embryo, where nests containing from four to sixteen closely 

 packed nuclei are very characteristic of certain early stages. 



CELL DEGENERATION IN A8TACU8 AND HOMARUS. 



Homaru/i americanu.1. — I find certain bodies' in the lobster essentially similar to those which 

 characterize the Alpheus embryo. If a longitudinal section of the egg uauplius of Uomarus bo 

 compared with Fig. 125, which represents a similar section of a similar stage of Alpheus sauleyi, we 

 find not a few chromatin balls, but a meteoric swarm of granulated bodies and naked chromatin 

 grains coextensive with the embryo, and reaching a considerable distance into the yolk amid the 

 scattered mesodermic cells, but perhaps most abundant, as in Alpheus, in the neighborhood of the 

 stomodaHim. A long nebulous train of yolk spherules and granules extends forward a consider 

 able distance in front of the mouth, and is especially marked in front of the optic disks. The 

 labrum and the folds of the appendages which contain yolk abound in these peculiar granulated 

 bodies. In less number they occur in connection with the endoderm cells, which have at this 

 stage extended through a greater portion of the egg and form a series of irregular sacs tilled with 

 yolk. Tlie.se yolk masses, with their surroundiBg sheet or advancing column of cells, correspond 

 to the endoderm sac of the crayfish. In the latter the jieculiar cell bodies also occur. 



If one now examines very thin" sections under high powers, we find that the granules and the 

 granulated bodies correspond in general to the structures we have found in Alpheus. The chroma- 

 tin grains appear sometimes as naked masses in the yolk ; sometimes they possess a distinct proto- 

 plasmic body. The degenerating chromatin stains either very intensely or faintly and is often 

 vesiculated; that is, it appears as a hollow shell. Under favorable conditions it is easy to demon- 

 strate the fact that thc^se bodies surround particles of yolk, and occasionally they have a crescentic 

 shaiie, when it can be clearly seen that they are enwrapjiing a yolk spherule. This vitelloi)hilus 



* While this memoir was in press a paper was received on Amilosit in the Embryonal KnreJopes of the Scorpion, by 

 H. P. JohiiHim, (Riillotiii of the MuNenm of Coiiipsiral.ivo Zoology, Vol. xxii, No. H). Only two inHtanooR of iliroct cell 

 division in tlio onibryo of Arthropods aro rcoonlcd : that fonml l>y Cnrnoy in tho vontral phito of /I i/drnph il im piceiin 

 and tbo caso \vhi<'li Wliocler has di^scribod for tho blaHtodprin of HIatIa germnnica. Mr. .Johnson linds that do-'cn- 

 eratiou does not always follow upon inilirect cell division, as iu the case of aiuitosis in the testicnlar cells of certain 

 Isopods. 



