PLASMA-STRUCTURE IN EGG OF HYDRACTINIA 219 



Again, Schaxel finds mitichondria already present in the early 

 growth-period of the egg before his 'chromatin-emission' occurs. 

 In this respect results with Hydractinia are different, since the 

 mitochondria appear only after the egg is a third grown. Hydrac- 

 tinia is an exception to the rule in this, since in most forms the 

 mitochondria are either aheady present or appear in the early 

 growth-period. The possibility of direct nuclear origin of the 

 mitochondria in Hydractinia is also excluded, since they arise 

 de novo throughout the egg and are not collected in a definite 

 body against the nucleus (yolk-nucleus) as described in many 

 forms.* The mitochondria in Hydractinia do no contribute to 

 the formation of the yolk, as described for other forms by a number 

 of workers.^ I also find no grouping of the mitochondria around 

 an idiozome, indicating their origin through the retrogressive 

 development of the' 'centroplasm' as suggested by Vedjovsky. 

 Again, Hydractinia gives no evidence of the mitochondria forming 

 a part of the architecture of the protoplasm (Faure-Fremiet and 

 others), since in centrifuged eggs they are carried to one pole of 

 the egg together with the yolk, leaving a free layer of protoplasm 

 which has the usual protoplasmic structure. Since the blasto- 

 mere of a centrifuged egg containing no mitochondria develops 

 into a swimming larva, they can hardly be vital units of the proto- 

 plasm. I find no indication of their multiplication by division 



■* A yolk nucleus of mitochondria is described in the eggs of the stint (Lams 

 '04, Arch. Anat. micr., T. 6); Rana (Lams '07, Arch. Anat. micr., T. 9); Proteus 

 (Schmidt '04, Anat. Hefte, Bd. 27, and M. Jorgensen '10, Festschr., R. Hertwig); 

 Testudo (Loyez '05, '06, Arch. Anat. micr., Bd. 8) ; chick (D'HoUander '04, Arch. 

 Anat. Micr., T. 7); some birds (Loyez '05, .'06, Arch. Anat. micr., T. 8); human 

 egg (Van der Stricht, '05, Bull. Acad. Belgique); cat, (Russo, '09, '10, Arch. f. 

 Zellfor., Bd. 4-5); bat and guinea-pig (Van der Stricht '05, Compt. Rend. Assoc. 

 Anat., Geneve); Ascaris (Schoonjans '09., Bull. Soc. Roy. Sci. Med., Brussels); 

 Ciona intestinalis (Loyez '09, Assoc. Anat., Nancy). 



^ Yolk is described as being formed directly from the mitochondria by Russo 

 ('09, '10) in cat; Loyez ('09), ascidians and human egg, Compt. rend. Assoc. Anat., 

 Paris; Faure Fremiet ('10, Arch. Anat. micr., T. 11); in Lithobius; Zoja ('91, 

 Mem. del R. Inst. Lomb. di Sci., vol. 16) etc. Yolk is described as formed indirectly 

 under the influence of mitochondria by Van der Stricht ('05) in the bat; Lams 

 et Devorene ('08, Arch, de Biol., T. 23) in some mammals; Van Durne ('07, Ann. 

 Soc. Med. de Gand, T. 88); Schooonjans ('09) Ascaris; Bluntschli ('04, Morph. 

 Jahrb., Bd. 32) etc. 



