260 J. E. S. MOORE. 



outside tlie physical domain, as ordinarily understood, is still 

 a fundamental, though quite legitimate problem for micro- 

 scopical inquiry. 



In attempting to obtain a clear conception of the premises 

 from which we have to start in such inquiries, the once 

 absorbing question of the nature of the wide structural differ- 

 ences often apparent in the male and female cells will be found 

 to have lost, if not much of its importance, at any rate most 

 of its original characters. The conjoint labours of Hertwig,^ 

 Ishikawa," vom Rath,^ and others, as well as the curious 

 observations of Weismann concerning the non-specialisation of 

 certain spermatozoa, have completely changed the scenes in 

 this direction; and it is matter for rejoicing that the shifting, 

 at any rate in this particular, tends towards a simplification in 

 the gradual banishment of apparent difference in such elements, 

 and of their associated mechanical complexity, to the rank of a 

 purely physiological importance. 



Opinion to-day is almost unanimous that the ova and 

 spermatozoa are strictly similar objects, that even the most 

 modified spermatozoon still carries about with it the dwarfed 

 representatives of cell structure; and our knowledge of its 

 development is sufficiently advanced to recognise in the head 

 the reduced nucleus, the kytoplasm in the tail; and lastly, it 

 appears probable from Hermann's,* and more especially from 

 rick's^ investigations, that the hitherto enigmatical "Mittel 

 Stiick" is in reality nothing less than the attraction sphere.^ 



' " Vergleicli der Ei und Samenbildung bei Nematoden. Eine Grundlage 

 fiir cellulare Streitfragen," ' Archiv f. mikroskop. Anat.,' Bd. xxxvi, 1890. 



2 ' Studies of Reproductive Elements.' 



3 « Archiv mikro. Anat.,' Bd. xl, p. 102. 



* 'Archiv fiir mikros. Anat.,' Bd. xxxiv, Tafel 3. 



* " Ueber die Befruchtung des Axolotleies," ' Anatomischer Anzeiger,' vii, 

 pp. 818—821. 



^ The results of a re-examination of the facts of Mammalian spermatogenesis 

 have shown that the centrosomes are incorporated in the spermatozoa in the 

 position of the Mittelstiick of Amphibia, while a portion of the archoplasm 

 is applied to the pointed extremity of the head. Field has shown that the 

 archoplasm "Nebenkern" of Echinoderms is incorporated together with the 

 centrosomes as the Mittelstuck. 



