The Spermatogenesis of the Opossum (Didelphys virginiana) etc. 61 
much attention from French Belgian (notably Duesberg, Lams, and 
Samssonow), German (Meves, Hertwig, Goldschmidt, Popoff, and 
Büchner) and several Russian workers (Rubaschkin and Tschaschin). 
In 1902 Hertwig introduced the term “chromidial-net” for extra- 
nuclear chromatin in Actinospherium. Its real meaning was qnite obscure. 
In 1904, Goldschmidt described certain curious chromatin Strands in 
muscle cells of Ascaris. These he called “chromidial apparatus” and descri- 
bed them as extruded from the nucleus. In 1907, Popoff described 
“chromidia” in the spermatocyte and ovocyte of gasteropods ( Paludina 
vivipara). These he interpreted as chromatin granules extruded from 
the nucleus. On the basis of his later observations on Helix he States 
his conclusion “that the structures described by various authors under 
the names of mitochondria, pseudo-chromosomes, archoplasm, ergasto- 
plasm, Nebenkern, idiozome (only in certain cases) and idiozome remains, 
are referable to different stages of one and the same developmental series 
of chromidia” (quoted from Dobell). To say the least, this list is pro- 
bably too inclusive. Dobell points out that the Nebenkern is frequently 
an attraction sphere. It is also doubtful whether archoplasm and er- 
gastoplasm (any more than myofibrillae) and idiozome (in many cases) 
shoidd be listed under “mitochondria”. Wassilieff (1907) also describes 
“superfluous chromatin” cast out of the nucleus in the spermatocytes 
of Blatta germanica and designates the same as chromidia and identifies 
it with mitochondria. It appears then that the chromidia hypothesis of 
Richard Hertwig (1902) took origin in protozoologv, and received its 
chief Stimulus to growth from the hypothesis of the binuclear nature of 
cells, so ably advocated by Goldschmidt. The mitochondrial hypothesis, 
on the other hand, took its origin in the field of gametogenetic cytology. 
Now that chromidia and mitochondria have become identified, the main 
discussion Centers upon the question of the source of origin of these bodies. 
This involves attack and counter-attack on the several theories constructed 
by the rival schools on the basis of their supposed origin and fate. A 
nuclear origin is strenuously maintained by Hertwig, Goldschmidt 
and their students, and the theory of Kern-plasma-relation ably defended. 
A cytoplasmic origin is just as strongly defended by Meves, Duesberg 
and their students, and the hereditary value of cytoplasm (as opposed 
to chromatin) ably mged. Duesberg denies identity between mitochon- 
dria as defined by him (integral parts of cytoplasm) and the chromidia 
of Goldschmidt (strictly defined as nuclear extrusions). 
Before stating the views in full of these two rival schools and their 
adherents it may be well to give a list of the structures now generally 
