68 



in the tribe, and that they also occur in the Hepaticae. Mnium 

 hornum, common on sandy banks, affords a good example for obser- 

 vation about this time of the year; but it is necessary to observe that 

 the antheridia must be watched, and taken at the proper moment, in 

 order to obtain results which shall be perfectly satisfactory. They 

 continue in perfection for some days when confined in a tin box, but 

 probably burst more speedily in a growing state. It would seem that 

 the motions of the spirilla, both as to kind and intensit}-, are very 

 much influenced by the degree of maturity of the anther under exa- 

 mination. In an early stage, only a few of the spirilla among the gene- 

 ral mass show signs of activity, and their movements are comparatively 

 languid and fitful. In a perfect state the spirillum acquires both a 

 rotatory and a progressive motion, both motions, however, resulting 

 froui one and the same impetus. In a less complete state the motion 

 of the spirillum is either gyration on a fixed axis or one combined 

 with an irregular oscillatory movement, more or less rapid, varying 

 from two to ten or more gyrations in a second. The normal move- 

 ment, however, is in the direction of the spiral fibre, which screws 

 itself along through the fluid, often in a perfectly straight course, 

 dragging after it the sausage-shaped body ; the progressive motion 

 being often so quiet as to render it difficult to follow it. 



There has of late been a strong tendency to refer such movements 

 to some principle not distinguishable from that of animal life, but it 

 appears to me that they can be sufficiently accounted for on more 

 simple grounds. Were the spirilla really possessed of life, one might 

 expect them, at any rate, to follow the usual rule, and to go head 

 first, but these always move as if the spiral fibre were propelled by a 

 vis d tergo, and indeed the spiral fibre may be designed for the special 

 purpose of modifying the direction of the impetus from behind. It is 

 quite legitimate to assume that at the time of maturity the sausage- 

 shaped body is a membranous sac, filled with dense mucilaginous 

 matter, and that by the action of endosraose the bulk of the contained 

 mass is increased until a supply for a continuous jet, from a small 

 pore at or near the back of the body, and nearly in the direction of 

 the axis of the spiral fibre, has been produced. Such a jet would 

 certainly account for the movements, and is in perfect harmony with 

 what I have seen ; for I believe I have several times seen the jet 

 itself, but on this point I am willing to wait for further and more 

 decisive evidence. The possessors of better and more powei'ful 

 microscopes than mine are requested to pursue the subject. 



As to the function of the spirilla, I believe .it will be found in 



