252 Ellis. — The Life-history of Bacillus hirtus. 
agent or agents may be, their effect is seen in a slightly older culture where 
free spores vastly preponderate. Fig. 44 thus represents the final stage. 
In the last two stages a differentiation of the spore-coat into exine and 
intine can be observed. This differentiation is first observed in Fig. 42, but 
the markings of the exine cannot be ascertained till examined either at the 
Fig. 43 or the Fig. 44 stage. 
This description agrees with that given by Meyer for the development 
of the spore in Bac. Asterosporus (9), and by myself for the development of 
the spore in the genus Sarcina (3). There is one point, however, to be 
observed. Meyer introduces the term ‘ Sporenvakuole 5 as indicating the 
clear space in which the spore is formed, and in my former work I have 
followed the nomenclature. It seems to me, however, that we are not deal- 
ing with a ‘ vacuole/ but rather with a ‘ cell/ and this clear space, containing 
a nucleus and cytoplasm, is of the nature of a cell, and the process is that of 
free cell-formation, so that the clear space should be referred to as a 4 Spore- 
cell 5 rather than a ‘ Spore-vacuole/ for in the ordinary acceptation of 
the term a c Vacuole’ means a space filled with cell-sap. There are still 
several gaps connected with the development of the spore which are 
not yet bridged over. The history of the nucleus which serves as the 
nucleus of the spore is the most important. Does it migrate into the clear 
space, being cut off by division from one of the outside nuclei, or is it 
a nucleus of the cell, around which a clear space has been formed, 
marking the boundary of the new spore ? 
This and other problems will not be settled until higher magnifications 
than we possess at present have been placed at our disposal, or until more 
ingenious methods of observation have been arrived at. 
Motility and Ciliation. 
The name Bacterium hirtum was given to this form by Henrici (7), 
because when isolated it was found to be absolutely immotile. In an 
earlier paper I have shown that any non-motile form can be made motile 
by continual inoculation, and that immotile forms of Bacteria (excluding the 
thread forms) can be made motile by the same method (2). I applied this 
method to this form (1) and found that it became motile. On making cilia- 
preparations, the cilia were found to be situated at the poles, and the name 
of Bacterium hirtum , in accordance with Migula’s classification, was changed 
to Pseudomonas hirtum. Since then, however (1903), I have kept this 
form under cultivation for nearly three years and have made a special study 
of its motility and ciliation. Under continual inoculation the motility 
once gained has never been lost, but the ciliation is undoubtedly peritrich 
and not polar, so in accordance with this fact, this form must be allocated to 
the genus Bacillus. 
The first indication of motion is seen in a seven hours old culture. As 
