CONTRIBUTIONS TO THE CYTOLOGY OF THE JJACTEEIA. 451 



(c) Spirilla with Spherical Nuclei , 



The fourth and last spirillar form concerning whose 

 structure I have reached definite conclusions is exceedingly 

 minute. It is an organism which occurs commonly in the 

 hind gut of the common cockroach (S. orientalis) in com- 

 pany with the larger form already described. 



The organism in question has the characteristic form of a 

 small Spirillum or Vibrio (figs. 121-132, PI. 18). The 

 smallest Vibrio forms have a length of rather less than 2^i 

 (fig. 132) and upwards. In the hirgest Spirillum forms 

 the length rarely exceeds 4*5 fx (fig. 130). In all cases the 

 organisms are very narrow — the largest liaving a breadth of 

 approximately 0'5 fj, the smallest, considerably less. Yet, in 

 spite of their very small size, these organisms possess an 

 internal structure which may be demonstrated with the 

 greatest clearness. 



I have obtained very good results with wet films, fixed 

 with sublimate-alcohol and stained with Heidenhain. All 

 the figures (figs. 121-132) on PL 18 are from individuals 

 treated in this manner. Differentiation may be obtained 

 with comparative ease. 



Every individual — when properly stained — shows a single, 

 darkly staiiiing, sphei'ical body situated somewhere within it 

 (cf . figs. 121-124, 130-132). I regard this body as a nucleus. 

 This body — or, as I shall call it, this nucleus, may lie in the 

 centre of the cell (fig. 123, etc.) or at one extremity (fig. 121), 

 or in an intermediate position. It always has the form of a 

 minute round or oval granule, which appears — under the 

 highest magnification which has been available — quite homo- 

 geneous. It is a constant morphological feature of every cell. 

 No cytoplasmic structure can be made out with absolute 

 certainty, on account of the very small size of inost of the 

 organisms. Faint indications of an alveolar structure seem 

 to me, however, to be sotnetimes present. In addition, it 

 may be noted that the ends of the cells frequently stain 

 deeply, so that in optical section an individual often appears 



