SYSTEMATIC DESCRIPTION OF SPECIES. 77 



organism creeps about on the surface of the algae present 

 in the water. Cantacuzfene distinguishes three kinds 

 of individuals : i , slender forms (/* in breadth) , the axial 

 filament of which did not extend quite to the extrem- 

 ities; 2, shorter, thicker forms (i to i%p in breadth), 

 exhibiting no axial filament and sometimes occurring in 

 small masses; and 3. a few specimens showing a central 

 swelling, some 2^ in thickness, in which all the chro- 

 matin was collected, though the rest of the organism 

 stained darker than did the other forms. Sometimes 

 two swellings were seen, one to the right and the other 

 to the left of the central point. 



SPIROCH^ETA BALBIANII. 



(Trypanosoma balbianii, Certes, 1882.) 



This large spirochsete was first described by Certes 

 in 1882, though it had been previously seen by Moebius. 

 It is found in the crystalline style of the oyster (Ostrea 

 angulata, 0. edulis). It attains a length of 100 to i2o/x 

 and a breadth of 5/x (extremes 26 to zoo/* in length; 

 3 to 5/1 in breadth, Perrin). Perrin describes an in- 

 different form, a female form, and male and female 

 gametes. Taking the so-called indifferent form as 

 typical, the general proportions being those described 

 above, the organism consists of a periplastic sheath with 

 fluid protoplasmic contents. The former is of some- 

 what firm consistency, retaining its form when the 

 contents have escaped. It is furnished with an un- 

 dulating membrane, running spirally round the body 

 (Fig. 2). This has a dark peripheral fibre (border fibre, 

 randfibrille) or thickening of the edge of the membrane. 

 There is a dark nodule at each end of the periplast. 



The nucleus consists of a spiral band (karyosome) 

 formed of achromatic substance with bars of chromatin 



