396 
Spirochaetes of Tapes aureus 
previously stated (I. 1908, p. 13), the cytoplasm does not usually stain 
at all deeply with most “ plasma ” stains, Lichtgriin excepted. 
At each end of the organism is a basal granule (“ calotte ” of 
Swellengrebel) which stains like chromatin. Gonder (1908—9) has 
recently found basal granules in S. pinnae. 
Each Spirochaete possesses a membrane (the “ undulatory membrane” 
of many authors, or the “ periplast appendix and chromatic band ” of 
Swellengrebel), which is a spirally coiled lateral extension of the peri¬ 
plast, and contains myonemes. The membrane is contractile, and is a 
locomotor organella. 
The relation of the membrane to the body of the Spirochaete is 
seen on examining sections of the parasites (PI. VI, Fig. 54), obtained 
on cutting sections of the crystalline style of an infected Lamellibranch 
(cf. Fantham, I. 1908, p. 30, Text-fig. 6). In cross-section the periplast 
of the Spirochaetes is somewhat retractile and stains rather deeply. 
These characteristics of the periplast are probably due to the presence 
therein of a chitinoid substance. The periplast is firm, yet very 
flexible, strength and power to bend both being due to its physical and 
chemical nature. 
The Various Spirochaetes of Tapes aureus. 
On examining a preparation from an infected style of T. aureus 
(Tapes, No. 1), fixed wet with Bouin’s liquid and stained with iron- 
haematoxylin, three forms of Spirochaetes could usually be seen in 
any one field of the microscope. Although intermediate forms occur, 
we may for convenience’ sake divide the prevailing farms into three 
groups, A, B, and C :— 
Group A includes very thin, undulatory Spirochaetes, with well- 
marked membranes, and bodies from 30/u. to 60/x long, and about OSyu, 
broad (Text-fig. 2 A, PI. VI, Figs. 1—5). 
Group B includes long, somewhat thicker Spirochaetes, usually with 
pointed ends, well-marked edge to the membrane and a tendency to 
have flattened spirals (Text-fig.-2 B, PI. VI, Figs. 13, 15—21). These 
parasites are from 50^t to 90p, long, and 1/r to 1’3/i broad. 
Group C includes shorter, broader forms (Text-fig. 2 C, PL VI, Figs. 
35—37), with membrane sometimes well-marked, sometimes closely 
contracted around the body, which is from 50/z to 70/x in length and 
about 2/u, in breadth. Usually only a few waves, of relatively large 
amplitude, occurred along the body. 
