176 THE NORTHERN MICROSCOPIST. 

forms are, the cycle of their history is as rigid along inherited lines, 
and by means of specificially specialised function, as are those of 
an Agaricus or a rose. De Bary finds that Achlya prolifera is 
reproduced by alternate methods like vaucheria. The asexual 
spores accumulate rapidly at the apex of the thallus, which ulti- 
mately bursts, and sends the spores forth by thousands, possessed 
of cilia and motile power, to germinate and grow. 
But the ultimate preservation of the vitality in the plant depends, 
as ever, upon fertilised spores. The process is seen in Plate II, 
Fig. 5, which is a thread of the thallus. a is a branchlet, bearing 
a sac-shaped cell, in which the protoplasm collects and swells into 
a globular form, 4, while arms at d, c begin to show themselves. 
Soon a septum forms, as at e, making the cell separate ; the anther- 
idium tubes, f, g, are by this time lengthened and closely applied 
to the cell; the nuclei resulting within the ceil now strongly con- 
tract, and after fertilisation by the antheridia, these surround them- 
selves with a cell-wall. An illustration from Cornu of Achlya 
racemosa shows, at /, 2, the separated cell or oogonium, and at m 
the action on this of the antheridia tubes is manifest. The same 
is seen at 7, 0, in another illustration ; but is more delicately shown 
by De Bary by the combined action of the antheridia and the 
oogonium of Peronospora, as at &, 2 
Now the speciality of this case, in my illustrative evidence of the 
fallacy of the attempt made by some amongst us whose industry 
we respect, to establish evidence of ‘“‘ Heterogenesis,” from their 
observations is this, viz., that it enables me to point out one source 
of the error of inference; that is, want of knowledge of the life- 
histories of the forms from which inferences are made. One of 
the illustrations placed before this society in ‘‘ proof” of the hetero- 
genetic origin of living things was what was called a saprolegnia 
growing on the body of a dead fly in the water. The fly had been 
attacked by fungus on a window pane and died. _It was put into 
water and the result watched. Without doubt Mr. Berkeley would 
have anticipated the result, but it was not so in this case. The 
saprolegnia grew apace, spread in all directions, and soon there 
arose visible circulation of protoplasm within the thallus, and 
minute granules were carried in the stream. 
The inference made from this was, that the “ protoplasm” of 
the dead fly’s leg, had directly changed itself into the protoplasm 
of the saprolegnia, and was in visible circulation there. 
But for the persistence with which this “‘ heterogenetic fact” has 
been presented both at the Microscopical Society of Liverpool and 
at this Society, it would seem needless to repeat the facts; but in 
the interests of the younger students and workers it is needful. 
Originally this fungus, which attacks the fly in the air, was called 
by Cohn, Empusa musce. By Fries it was called Sporendonema 


