H. B. Fantham 
401 
exhibited by the “ indifferent ” individuals would necessitate a re¬ 
classification of these forms, some probably being assigned the attributes 
of the “male” sex (Fig. 10), while others would probably be termed 
“female” (Figs. 29—32)—an unsatisfactory procedure. Such an im¬ 
portant matter as the existence of sexual polymorphism in Spiro- 
chaetes cannot be decided by the examination of stained specimens 
alone. It is essential that it should be determined by the examination 
of the living organisms. Although I have examined many hundreds 
of living Spirochaetes from Tapes aureus I have never seen one that 
exhibited any sexual attributes, and until actual conjugation of the 
living organisms has been witnessed, I believe that it is useless to 
assign the attribute of sex to any form of Spirochaete. The hypothesis 
of sexuality, as explaining the morphological differences exhibited by 
the Spirochaetes of Tapes, is, in my opinion, quite untenable. 
(c) The Hypothesis of true Morphological Variation due to Division 
and Growth. The various forms of Spirochaetes from Tapes aureus may 
be broadly classified as being long (PI. VI, Figs. 5, 15, 18, 19, 20, 33), 
or short (Figs. 1, 8, 9, 11, 12, 34), narrow (Figs. 1—5), or broad (Figs. 
35—37), or as possessing ends that are pointed (Figs. 17, 19, 20, 21), 
tapering (Figs. 15, 32, 35), or round (Figs. 14, 30, 34). 
The differences in length of the Spirochaetes are explicable by the 
direction of division. Transverse division of a long thin individual 
(PI. VI, Fig. 5) results in the formation of two short daughter forms 
(Figs. 1, 2), while somewhat broader forms (Figs. 15, 18) that divide 
transversely (Figs. 50—52) produce individuals of medium length (Figs. 
14, 17), about half that of the parent. Growth in length of the 
daughter forms occurs producing individuals similar to those shown in 
Figs. 16, 21, 25. All gradations in length are explicable as being 
due to transverse division followed by the growth of the daughter 
organisms. Marked variations (50p. to 150^.) have also been recorded 
in the length of S. halbianii in the oyster by all workers who have 
studied that parasite. 
Variations in breadth are produced by longitudinal division. 
Moderately broad individuals divide longitudinally (PI. VI, Figs. 39, 
40, 42) and the daughter forms are about half the breadth of their 
parents (Figs. 7, 8, 42). Very narrow forms also divide longitudinally 
(Figs. 43, 44) and give rise to fine, almost hair-like Spirochaetes 
(Figs. 1—3). Longitudinal division of thick forms produces parasites 
of medium breadth. 
Variations in length and breadth of the Spirochaetes of T. aureus 
are due then to growth and division. Thin forms (type A)—resulting 
