It's the spirilloe of a water plant.

Move on to the next." Tom, in much perturbation of mind, shuffled down the line and looked through the next brazen tube.

"This is a preparation of stomata," he said, recognizing it from a print in his book on botany.
The professor shook his head despondingly.

"You are right," he said; "pass on to the next." The third preparation was as puzzling to the student as the first had been, and he was steeling himself to meet the inevitable when an unexpected circumstance turned the scale in his favour.

It chanced that the other examiner, being somewhat less of a fossil than his _confreres_, and having still vitality enough to take an interest in things which were foreign to his subject, had recognized the student as being the young hero who had damaged himself in upholding the honour of his country.