76 



Mr. L. Hogben. 



legists have been very hesitant to admit the passage of material from the 

 nucleus to the cytoplasm ; partisans of the mitochondrial and chromosome 

 hypotheses have been equally eager to disclaim any such suggestion. That 

 the plasmosome plays an important metabolic role in oogenesis, and in a 

 number of cases actually secretes fluid or solid particles that pass as such into 

 the cytoplasm is, however, clearly indicated by the recent work of Hempel- 

 mann(15) and Buchner(16) on the Archiannelid Saccocirrus, Dendy on 

 Grantia, and the testimony of numerous writers who have lately examined the 

 secondary nuclei of the Hexapod egg. While some confusion arises by the 

 use of the term " chromatin " (17) for such particles, since structurally 

 the plasmosome and chromatin are separate and no valid chemical tests 

 indicate their identity, it now seems possible to place the whole question of 

 the transmission of nuclear material to the cytoplasm with the genesis of 

 the secondary nuclei upon a basis which is not incompatible with what is 

 generally accepted regarding the behaviour of chromatin and mitochondria in 

 the germ cycle.* 



Buchner, in particular, traces the origin of secondary nuclei in the 

 Hymenoptera to the plasmosome; and the author has recently examined 

 preparations of the ovaries of Croesus, one of the Tenthredinidse (unpublished), 

 in which this is certainly the case.f Now if the plasmosome is to be added 

 to the list of independent cell organs, as Carleton's work in itself strongly 

 indicates, it may seem at first highly improbable that bodies so closely 

 sunulating true nuclei as do the accessory nuclei of the Hymenoptera should 

 not be chromatinic in origin. Though characteristic secondary nuclei are not 

 found in Libellula, the behaviour of the plasmosome in this form, as also in 

 Anax and Plathemis, is here of great interest. It will be remembered that 

 the intranucleolar deutosomes of Periplaneta were said to have the appearance 

 of minute nuclei. In the nucleolus of Libellula, the oxyphil medulla (intra- 

 nucleolar deutosome) is at first of finely granular structure in fixed prepara- 

 tions. This is indicated in figs. 36, 37, but in illustration its extraordinary 

 resemblance to a nucleus cannot be reproduced in such a way as to do justice 

 to the original. In short, the oogenesis of Libellula shows that bodies may be 

 formed within the 'plasmosome itself which have as genuine a resemblance to true 

 nuclei as the secondary " nuclei " of the ffymenopteran egg : this reinforces the 

 evidence for regarding the latter as a product of the plasmosome; and the 

 undoubted emission of nuclear material during oogenesis no longer necessitates 



* Cytomixis in CEnotliera (Gates) merits re-investigation from this standpoint. 



t By tlie courtesy of Dr. Gatenby I have recently seen preparations of Apanteles 

 ■which show vacuolation of the plasmosome and presence of accessory nuclei in the 

 diplotene stage ; this leaves no doubt, in my mind, that the latter are nucleolar rather 

 than chromatinic in origin. 



