Helen Dean King 373 
idiozome is transformed into the middle-piece and not merely a part of 
it as in Amphiuma. The results of my investigation of the origin of 
the middle-piece do not agree with those obtained by any other investi- 
gator of amphibian spermatogenesis, although they accord with Calkin’s 
account of the origin of the middle-piece in Lumbricus. 
As far as I am aware, Fick (13) is the only investigator who has 
found that the middle-piece of the mature spermatozoén of amphibians 
shows any great capacity for staining either with chromatin or with 
plasma stains. Fick states that the middle-piece of the spermatozoon 
of Axolotl stains intensely black after the use of iron-hematoxylin, 
whereas in Bufo and in other amphibians it remains nearly colorless. 
This difference in staining reactions suggests that the inner centrosome 
in the Axolotl spermatozodn remains in the middle-piece and does not 
go into the posterior end of the head as it does in other forms. 
The history of the centrosomes in the spermatid of Bufo is similar in 
many ways to that of the centrosomes in the spermatid of Salamandra and 
of Amphiuma, yet it differs in several important respects. In Bufo, as 
in the Urodela that have been most carefully studied, the axial filament 
of the tail grows out from one of the centrosomes while the other passes 
into the posterior end of the head. Whether this latter centrosome takes 
any part in the formation of the middle-piece, as Meves has stated for 
Salamandra, I have not been able to determine. 
The history of the outer centrosome in the spermatids of Bufo is not 
easily traced as this body is small and loses its capacity for staining 
intensely at an early period. After the formation of the axial-filament, 
the outer centrosome wanders to the posterior end of the middle-piece, 
where presumably it remains. In the mature spermatozoon this centro 
some probably serves as an “end-knob,” as in the great majority of 
cases the connection between the two centrosomes, shown very clearly at 
the stages of Figs. 60-63, is broken before the spermatozodn becomes 
mature. I have never found the outer centrosome elongated as if it 
were in the process of division, neither have I found the ring-shaped 
structure around the axial-filament that is so conspicuous in the sperma- 
tids of Salamandra and of Amphiuma. The outer centrosome in Bufo 
behaves very much like the portion of the outer centrosome in the 
Urodela that remains at the posterior end of the middle-piece. This 
suggests the possibility that Hermann (21) is right in considering that 
the ring-shaped structure around the axial-filament in the spermatids of 
Salamandra is not derived from the centrosome. Herman states that 
the ring is formed from the mid-body of the last spermatocyte division ; 
