500 On Spirocliseta (Trypanosoma) Balbiauli, dx. 



with the membrane discontinuous in tlie centre, where a 

 vacuole-like space occurred ; the edges of this space were 

 sharp, not torn, while the periplast appeared just continuous 

 over the gap. Laveran and Mesnil [5] have described trans- 

 verse fission. I think this mode of division naturally occurs, 

 and such cases are not to be explained away [8, 9] as merely 

 two forms which, having divided longitudinally, are now 

 separated by 180°, just before complete separation. Further, 

 in living specimens one sometimes sees forms vibrating about 

 a node, possibly not central, but I have never seen in life 

 division about such a point. 



Affinities. 



Spirochaetes are Protists : doubtless all will agree to this. 

 Next arises the vexed question, Are they Protozoa or 

 Bacteria ? 



Their diffuse nuclei and transverse fission rather suggest 

 Bacteria; while, on the other hand, the presence of an undu- 

 lating membrane, longitudinal fission, and even definite 

 *' chromosomes " suggest Protozoa. Perhaps, too, their size 

 is great for Bacteria, though too much importance must not 

 be attached to questions of size probabl3\ 



I am not at all sure about the presence of male and female 

 forms [8, 9] or of encystment [8, 9]. I think these appear- 

 ances can be otherwise interpreted, the male and female forms 

 being possibly the extremes from a more or less continuous 

 series. 



On the whole, I somewhat incline to the Protozoal nature 

 of these organisms, but prefer to leave further discussion of 

 this and other points for my longer illustrated memoir, which 

 will, I hope, appear in the Quart. Journ. Microsc. Sci. 



Postscript. — To this preliminary account it might be of 

 interest to add that Spirochceta Balbianii was found moving 

 about freely in a basin of sea-water in which specimens of 

 infected English oysters were kept, the shells of these oysters 

 being still partly covered by mud from their native beds. 

 I was able to demonstrate this, with living specimens, to 

 some of my friends. 



I have also examined specimens of the Acarid, Atax Bonzi, 

 Clap., found in the mantle-cavity of Anodonta, but have not 

 yet succeeded in finding any Spirochaetes in the Acarids, 

 although Spirochceta Duttoni occurs in ticks. 



