402 
Spirochaetes of Tapes aureus 
from the longitudinal division of broader forms—are capable of growth 
in length and thickness and become Spirochaetes of the B type (PI. VI, 
Figs. 15, 18, 19). Transverse division occurs in the B forms (Figs. 
50—52), and the daughter organisms, either directly or by growth in 
thickness, give rise to parasites of the C and D types (Figs. 28—37). 
It is among the D forms that longitudinal division is common (Figs. 
39, 40). 
Differences in the shape of the ends of the Spirochaetes examined 
are probably due, in part, to slight differences in the process of transverse 
division. Sometimes the parent forms seem to elongate slightly and 
then gradually to constrict in the middle (PI. YI, Figs. 49, 50). The 
resultant daughter forms would possess tapering ends (Figs. 9, 16). 
Parasites with tapering ends resemble the S. balbianii figured by Certes 
(1882) from oysters at Arcachon and La Rochelle. In some specimens 
the dividing Spirochaete seems to constrict more suddenly without 
much increase in length (Fig. 51). The daughter individuals from 
such a division have one end slightly more rounded than the other 
(Fig. 26), the rounder end being the one formed at the point of fission 
of the parent. Again, very gradual elongation and constriction of the 
dividing Spirochaete may occur (Fig. 52), and the individuals resulting 
from division tend to have at least one end pointed (Fig. 17), namely, 
that end formed by the breaking across of the elongate, median con¬ 
striction of the parent. 
In view of the many differences of form directly attributable to 
the processes of growth and division in Spirochaetes, I conclude that 
true morphological variation is sufficient to account Tor any form of 
Spirochaete that has been observed in Tapes aureus. Consideration of 
the series of the figures set forth in Plate VI, justifies this conclusion, 
at any rate in the present state of knowledge. 
Marked morphological variation is not unknown among the parasitic 
Protozoa. Good examples of such variation may be found in various 
species of Cnthidia and Herpetomonas, so that the occurrence of morpho¬ 
logical variation among Spirochaetes is not surprising. 
The possible Infection of Tapes aureus with Spirochaeta 
balbianii directly from Oysters. 
The specimens examined from the first batch of Tapes aureus 
received by me at Banyuls were found to be uninfected with Spiro¬ 
chaetes. Oysters were also obtained locally at Banyuls, and most of 
them were found to be infected with S. balbianii (PI. VI, Fig. 38). 
