130 J- Moore, 



that the cyst-cells stand in the same relation to the cyst as do the 

 foot-cells to the mammalian tubule. 



A complete account of the histogenesis of the mammalian testis 

 would be an immense acquisition to our knowledge, not only because 

 it would almost certainly clear up this discrepancy, but because it 

 would furnish the basis for a clearer conception of the reproductive 

 cell in general. 



I am personally of opinion that no wide generalizations can be 

 arrived at in these matters (at any rate with that degree of proba- 

 bility which can alone make hypotheses of any practical value) until 

 the course of development in a great number of spermatogenetic types 

 has been followed out with modern exactitude. My own experience 

 has taught me that the spermatogenetic process is singularly prone to 

 variation, even as involving those very characters which any one who 

 had confined his studies to a single type would certainly have regarded 

 as essential. The existence of this variation brings forcibly to mind 

 the possibility that insufficient data might lead to conclusions quite 

 as erroneous as our knowledge of invertebrate development in general 

 would have been, if studied only in the light of say; that of the sponges! 



Unfortunately, no sufficiently complete history is at present re- 

 corded even in a single type. Nearly all the current works on mam- 

 malian spermatogenesis deal exclusively with the general phases of the 

 process, and with the vexed question of the origin of the successive 

 crops of semeniferous cells. 



Brown 1) who has given in some ways one of the best accounts 

 we have, when speaking of the origin of the semeniferous elements, 

 asserts that the „spore-cells" (regenerative cells) divide probably by 

 akinesis, one half of the resulting elements presumably remaining in 

 the condition of the original spore-cells, and the rest, having acquired 

 new characters, dividing by mitosis to form "growing-cells" which in 

 turn become again divided by mitosis into small round elements, which 

 are each individually metamorphosed into a spermatozoon. 



Ebner-), in a more elaborate treatise, arrived at substantially the 



1) Qu. Jour., Micr. Sci. Vol. XXV. p. 343. 



*) Archiv für mikr. Anat. Bd. XXXI. p. 236—289. 



