MOETALITY IX PIKE-PEECH EGGS IX HATCHERIES. 7 



and it becomes a question whether these should be reo;arded as cells 

 or not.- On the other hand, at the 29-hoiir stage, abnormal eggs 

 are often segmented into such small cells in such a way that, exter- 

 nally, it is very difficult to tell them from normal eggs, although in- 

 ternally they may be shown to be very irregular in behavior. The 

 intermediate stages are therefore the best material for this phase of 

 the investigation. 



Those cytological features in the development of normal eggs 

 which bear on the work in hand are as follows : Up to the 16-cell 

 stage cell walls are sometimes partially or completely absent, but 

 asters and spindles are normal in size and occupy the same position 

 that they would if there were a distinct separation into cells. Fol- 

 lowing the 16-cell stage, the cleavage, which becomes externally com- 

 plete at least in the surface layer of cells, gives evidence of this fact 

 internally by the presence of very distinct cell walls. Mitosis is at 

 first synchronous in all the cells, but this regularity is soon lost, so 

 that certain cells of an e<^^ ma}' be in the resting condition while 

 neighboring cells may be undergoing mitotic division. 



As already indicated, cytological examination of uncleavecl eggs at 

 4 to 8 hours showed the majority to be normal (fig. 11, p. 5). The 

 few exceptions were found to have anomalous mitotic figures, and 

 their number was increased in the 8-hour stage. At 29 hours every 

 uncleaved eg^ shoAved anomalous internal features. The exceptional 

 8-hour eggs often show a very large monaster (fig. 17, p. 5). Other 

 eggs may show several cy tasters and an occasional spindle (figs. 12 

 to 16, p. 5). At 29 hours no such large monasters are found in eggs 

 of this type or in those called abnormal and generally there is only 

 an increase of cytasters in the former. 



The abnormal eggs often present a curious mixture of spindles 

 and asters of varying sizes, drawn-out nuclei, chromosomal irregu- 

 larities, and partially formed cell walls (figs. 12 to 17, 21, and 22). 

 Frequently an egg is found in which a part has undergone regular 

 cleavage while the rest is filled with cytasters and shows no indica- 

 tion of cell walls (fig. 15). As it was expected that such irregu- 

 larities would be reflected in the distribution of the chromosomes in 

 division, evidence of such chromosomal abnormalities was sought. 

 But, as in other teleosts, the chromosomes are usually so clumped that 

 an exact analysis of them is very difficult. In at least one case, how- 

 ever, the metaphase plate in one cell showed close to 30 chromosomes 

 (which seems to be the diploid number as obtained from counts in 

 normal eggs. fig. 20). while the adjoining cell contained only about 

 15 (figs. 18 and 19). This might be explained as a case of partial 

 fertilization, in which the sperm has instigated a division of the 

 egg nucleus and later has fused with one of the nuclei resulting from 

 this first division of the egg nucleus. The fusion nucleus would then 

 be diploid and the purely maternal nucleus haploid. ^ 



Irregularities in cleavage and mitotic figures practically identical 

 with those here described have been obtained experimentally by a 

 number of investigators. It will be noted that in every experiment 

 of this nature the effect is to induce development with one of the 



- Reitrharcl (ISOOai mentions excrescences as occiirrinjr in correlation ^^^th the flow of 

 protoplasm in the formation of the protoplasmic cap. Since the number of egKS showinjr 

 the excrescences mentioned above increases long after the formation of the cap, in our 

 case, the phenomenon described bj' Reighard is probably not related to it. 



