808 KEPORT OF COMMISSIONER OF FISH AND FISHERIES. [14] 



ON THE RATIONALE OF RETARDATION. 



Every developing ovum is made up of certain cellular elements, each 

 one of which is provided with a central nuclear body, which appears in 

 the light of recent researches to be the directive dynamic center of all 

 further changes involved in the successive cleavages undergoDe by the 

 cellular elements constituting that portion of the egg immediately con- 

 cerned in the formation of the embryo. The assumed disappearance of 

 the nucleus of the egg has been proved not to take place in the act of 

 impregnation, in not only invertebrate ova but also in vertebrate ones 

 as well.* 



The hypothetical assumption of a Cytode or Moneron stage of develop- 

 ment in the ova of all forms by Haeckel does not, therefore, api^ear to 

 be sustained by facts. These and other known facts, such as the recent 

 observation of the metamorphoses of the nuclei of Ebizopods4n the 

 act of division (multiplication) also throws doubt on the existence of 

 the Monera themselves, as Hensen has suggested.! Xuclear networks 

 inside of cells, as well as intranuclear networks, seeui to be of almost 

 universal occurrence, according to the researches of Flemming, Klein, 

 the Hertwigs, Pfltzner, Fol, and others on animals and man, and by 

 Strasburger on plants. Indeed, so strikingly is this true that Stras- 

 burger has been tempted to utter the dictum omnis nucleus e nucleo, 

 which in English means that all nuclei originate from pre-existing nuclei, 

 just as formerly Schwann expressed himself to the same efi'ect in rela- 

 tion to the genesis of cells. Such intracellular granular networks ex- 

 tending outwards from the nucleus through the protoplasm enveloping 

 it may be seen well developed in the coarse vesicular connective tissue 

 cells of the American oyster, of which I have mounted preparations. 

 Vastly more complex intranuclear reticuli are found in the nucleus of 

 the unripe eggs of the common slipper-limi^et, Crejndula glauca. I have 

 seen the granular threads in these undergoing the most wonderful active 

 changes of form. Spindle-shaped nuclei, the opposite poles of which 

 were joined by granular threads, have been observed in the eggs of 

 Elasmobranch tishes by Balfour. These were in the act of division, or 

 in the diastole condition spoken of by Flemming. QEllacher has seen 

 granular threads radiating from the nuclei embedded in the cells of th. 

 germinal disk of the trout in its early stages of development. These 



* This disappearance is more apparent than real, and while the nucleus may disap- 

 pear temporarily it soon reappears, showing that nuclear matter still exists in the 

 cell in a concealed or disguised form. 



t A. Brass has receutlj' demonstrated the presence of a denser central body in some 

 of the so-called Monera by the use of reagents ; this central body he regards as answer- 

 ing to the nucleus, while his studies also show these organisms to be far from homo- 

 geneous. Huxley, in 1877, had doubts as to the constancy of this distinctive character 

 of the Monera; see j). T.^ of his Anatomy of the Invertebi'ates. The Hertwigs have 

 since shown the Faraminifcra to be nucleated, and Leidy has shown that a nucleus is 

 not always absent in some types, as in Biomyxa, for example. 



