[35] EMBRYOGRAPttY OF OSSEOUS FiSHES. 489 



Their appearance at this time reminds one of an exceedingly miuate 

 bnndle of cigars, transparent, and now forming the poles of the very 

 elongate nucleus. By this time the equatorial division of the cell into 

 two is i^ractically completed and at right angles to the axis of the con- 

 trolling center or nuclear body just described. The retrogressive or 

 resting stage now supervenes. The two poles with their bundles of 

 refringent rods are now the nuclear centers of two new cells which have 

 been the result of the cleavage. These two bundles of refringent rods 

 undergo a retrogressive metamorphosis, by which they become globu- 

 lar and take up a larger space in the center of the new cells of which 

 they form a part. The refringent rods disintegrate and the new nuclei, 

 which have passed into the resting or quiescent stage, undergo a repe- 

 tition of the changes above described during the next stage of segmen- 

 tation. 



The rhythmical phenomena which a<?company these internal changes 

 are manifested in the outward changes of form of the protoplasm in- 

 volved. The cleavage furrows are usually developed with comparative 

 rapidity, accompanied by a tendency to heap up the i^rotoplasm of the 

 two new cells in a conical form. This conical form then gives place to 

 a more depressed one, which coincides with the resting stage. The de- 

 velopment of wrinkles in the cleavage furrows, as shown in Figs. 35, 

 3G, 39, and 44, are also to be referred to active movements of the ger- 

 minal matter, involving more especially the paraplasm or suj>erflcial 

 cell substance. In fact these appearances show that contractility of 

 the protoplasm is manifested during development. 



Pathological or abnormal phenomena arc also manifested during very 

 early stages of the segmentation of the germinal disk. Of such early 

 iriegular forms of segmentation, I have represented three in outline in 

 Figs. 36, 37, and 38. The ])roof that these are abnormal is the fact that 

 the protoplasm of the component cells has become brownish, more dis- 

 tinctly granular and dead. The symmetry seen in Figs. 9, 10, 35, 39, 

 and 44 is wanting. Such appearances are the preludes to the disorgan- 

 i-zation of the egg, and are as fatal in their results as the appearance 

 known as "rotten spawn" in ova freshly taken from the ovary. 



The "rotten spawn," by the way, is interesting as showing that ova 

 may become injured while still within the ovary. Microscopic exami- 

 nation reveals the fact that such ova contain masses of clotted or dead 

 plasma, which is brownish by transmitted light, or whitish like boiled 

 rice by reflected light. This dead or injured protoplasm may involve 

 portions of the yelk only or parts of the outer germinal pellicle as well, 

 and the existence of such a condition in a lot of ova- is sutficieut to war- 

 rant their rejection, tor, as a rule, when any eggs from a female fish 

 show this condition, the whole of her spawn is worthless. 



To return to the subject proper to this part of our discussion, it is 

 also important to note that the first cleavage furrows do not cut en- 

 tirely through the germinal disk. The proof of this fact we have in the 



