4G6 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [12] 



not bioii.!^lit ill contact with tlio male spermatic fluid the outer pellicle 

 of germinal matter retaiued the disposition shown in Fig. 1, with its in- 

 . eluded vesicles, but as soon as the egg was fertilized, or shortly there- 

 after, the vesicles were seen to grow larger and less numerous, because 

 the clusters were coalescing and apparently being expelled from the 

 germinal matter. So great was the influence of the presence of sperma- 

 tozoa that those eggs in contact with them began to change almost im- 

 mediately, while unfertilized ova retained their vesiculated germinal 

 layer nnchaiiged for four hours after their removal from the ovary of 

 the i)arent lish. 



The disappearance of the vesicles above described icas therefore an indica- 

 tion of the fact that impregnation had tal-en place. 



Since the foregoing was written the writer has observed similar phe- 

 nomena in the ova of Tylosiirus, Vacate, and Cybiunij in all of which the 

 development of the germinal disk is effected by the aggregation of the 

 germinal i)c]licle at one pole to form the germinal disk. The same is 

 true of the eggs of the branch herring, Poviolobus vernalis, and the shad. 

 The germinal pellicle is, moreover, part and parcel of the intermediary 

 layer of Van Bambeke, couehe hcematoycne of Vogt, and parablast of 

 Klein 5 the germ disk and the yelk hypoblast are both derived from it, 

 as we shall learn farther on. It includes both of the latter, and the 

 names bestowed upon the cortical layer by diflerent embryologists sim- 

 ply serve to denominate what was at first a part of the germinal matter 

 of the Qgg and afterwards becomes the envelope of the yelk. 

 , Balbiani states that Agassiz and Burnett recognized evident traces 

 of segmentation in the unimpregnated eggs of certain American fishes 

 of the cod family. As tlie writer has been unable to find the original 

 of this statement, it will be of little use to discuss the matter in the ab- 

 sence of all evidence to confirm the observation, for, as not even a ger- 

 minal disk was developed in unimijregnated eggs of the cod after four 

 hours had elapsed, in impregnated ova it was appreciably developed 

 one and a half hours afterwards ; it follows that it is not probable that 

 any true cleavage of the germinal disk of this species ever takes i)lace 

 •without the influence of the spermatic particle. 



That the germinal disk is formed independently of the influence of 

 the spermatozoon in many other species there cannot, however, bo the 

 slightest doubt. I have witnessed this phenomenon in the eggs of Chi- 

 rostoma, Moronc, Parephippvs, and Ccratacanthns, while it is known to take 

 place in many other s])ecies investigated by European authors, but the 

 disk ai)i)ears in some cases at least to have been difl'erentiated before 

 it leaves the intraovarian cavity, as in some Salmonida', for example. 



In order to ascertain more definitely the nature of the minute vesicles 

 inclosed in the germinal layer, a number of unimpregnated ova were 

 jdaced in dilute acetic acid, M'hich had the ell'ect of freeing the outer 

 germinal pellicle from the yelk. The pellicle was then carefully removed, 

 and stained with hsematoxylon and mounted; the protojdasm interven- 



