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GEOFFREY SMITH AJ\ T D EDGAR SCHUSTER. 
break down into lumps and granules of chromatin which are 
attacked by phagocytes. The breaking down of the sperma- 
tozoa would appear to take place soonest in the region of 
greatest vascularisation. The germinal cells, or spermato- 
gonia lining the tubules, begin to be absorbed and to 
disappear very rapidly ; within six months there is no sign 
of them left. The gradual replacement of the degenerate 
tubules by fibrous tissue appears to take place chiefly by the 
ingrowth of invasive connecting tissue from the host at the 
region of attachment of the testis to the host's body. It is, 
however, impossible to be certain that some of the fibrous 
tissue in the centre of the testis is not derived from the 
connective tissue of the testis itself. 
In the cases of auto-transplantation, where the testes were 
simply severed from all their connections and left in the 
peritoneal cavity of the animal to which they properly 
belonged, a marked difference was observed in that the 
spermatogonia, or young germinal cells lining the tubules, 
so far from degenerating, remained alive, and after about six 
months showed signs of active proliferation. The ripe 
spermatozoa, on the other hand, undergo degeneration and 
replacement by fibrous tissue. The origin of this fibrous 
tissue would appear to be less from the surrounding area 
of attachment outside the testis than from the fibrous 
connective-tissue of the testis itself. 
We may compare these results with those obtained by other 
authors, especially by Foa (5) and Herlitzka (6), who both 
worked with Amphibia. 
Foa found that in frogs, testes auto-transplanted below 
the skin in the Ivmph-sac do not adhere, but that when 
placed in the abdominal cavity they always reattached them- 
selves, and became vascularised. All his experiments were 
apparently done as auto-transplantations, and did not last 
more than a month. He observed the partial substitution of 
fibrous for testicular tissue, but he makes no observations on 
the survival of the spermatogonia. His chief point is to 
prove the degeneration and disappearance of the ripe 
