[9] EMBRYOGRAPHY OF OSSEOUS FISHES.^ 463 



special physiological characteristics, about which it is very important that 

 practical fish-culturists should be informed, in order that they may be 

 enabled to handle the eggs intelligently. 



The existence of a second nuclear body in immature fish ova has been 

 asserted by Balbiani and Van Bambeke. Balbiani speaks of it as the 

 vesicule embryogene, a name given to it by ^lilne-Edwards, and he fig- 

 ures it in the immature ovarian eggs of Pleuronectes limanda^ lodged in 

 a depression at one side of the vitellus. He has also detected it in the 

 unripe ova of the carp, pike, i:)erch, and Cottus Icevigatus, by the use of 

 acetic acid. The writer has not seen this accessory vitelline nucleus in 

 the ovarian eggs of any species studied by him, although working with 

 the same reagent ; there is a possibility, however, that it may have been 

 ■gverlooked. This body corresponds to the accessory nucleus originally 

 "discovered by Von Wittich in 1845, in the eggs of spiders, and called a 

 vitelline nucleus {Botter-Tcern), by Oarus in 1850, which name is in gen- 

 eral use by German investigators 5 Van Bambeke speaks of it as the 

 nucleus of Balbiani. lleiterated attempts at a demonstration of this 

 accessory nucleus have failed with me ; I have seen what might be taken 

 for it, but would not venture to assert that what I saw was normally 

 characteristic of young ova, such as some of the investigators alluded 

 to above have evidently used. The immature ova of Anguilla vulgaris 

 have given me good opportunities to study the structure of the nucleus 

 or germinal vesicle, in which, however, I find nothing very different 

 from what has already been described by Beale, Eauber, and others. 

 The nucleoli adherent to the wall of the germinative vesicle in the ovi. 

 cell of the eel are, I find, very numerous. Amoeboid movements and 

 changes of form of the nucleolus or germinative spot have been de- 

 scribed by Eimer* in the immature eggs of Silurus glanis and the carp. 

 In these the germinative spot, which is included by the germinative 

 vesicle, underwent great changes of shape in comparatively rapid suc- 

 cession, throwing out prolongations in different directions, and then 

 withdrawing them again, like an Amoeba. The germinative six)ts of the 

 immature ova of Oambiisia show these movements. The germinative 

 vesicle itself, in fact, may undergo slight spontaneous changes of form, 

 and in stained preparations, especially where safranin has been used, a 

 considerable variation of form may be noted, and evidence of a thick 

 nuclear wall also becomes pretty clear in many immature ova. Nuclear 

 changes are, however, now known to be very generally manifested by 

 all kinds of cells. 



Kecently a more careful study of the germinative vesicle of ova in 

 general has revealed the fact that its substance is traversed by granu- 

 lar threads, which anastomose with each other and tend to connect the 

 walls of the vesicle and the germinative spot or spots together, just as 

 has been found to be the case with ordinary cells of all kinds where 

 the wall of the nucleus and the globular nucleoli are found to be joined 



*Arcl\.f. Mik. Anat., XI, 1875, pp. 325-32«. 



