36 PROGRESS OF MICROSCOPICAL SCIENCE. 
are seen—that is to say, only those which give rise by segmentation 
to daughter colonies. After a little time the number of colonies 
contained in each ccenobium diminishes, and then a great number 
appear with the androgonidia, which represent aborted daughter 
colonies. At this moment we find a few female groups not containing 
daughter colonies. After reproduction has gone on for some time by 
means of daughter colonies, we observe the number of female coeno- 
biums augment, and some composed exclusively of males appear, 
while the neuter sorts become very rare. M. Henneguy compares 
these facts with what occurs among plant-lice, which degenerate after 
the parthenogetic production has gone on for some time, and their 
digestive and generative organs tend to atrophy. Males are then 
produced, and, subsequently, females requiring fecundation. 
The Embryology of Cucumaria doliolum.—This has been described 
by Professor Selenka as follows :—After the formation of the single- 
layered blastoderm, and the embryo breaks through the egg-skin, it 
swims freely by means of its ciliated membrane. As the flagella 
gradually disappear, its activity is reduced to a backward and forward 
motion, and when the tentacles are protruded it sinks to the ground, 
and moves only by crawling. After fecundation the nucleus (Kern) 
diminishes, and becomes a mere drop of protoplasm, inside which a 
germinal speck (Kernhof) appears in an hour or two. The segmen- 
tation of the yelk goes on till 250 cylindrical flagellate cells are 
formed. ‘When the embryo emerges from the egg and swims in the 
open water it contracts itself in about twelve hours to about one-fifth 
of its diameter. Hereupon from its hinder pole, and below a flattening 
of the same, three to eight blastoderm cells project inwards. The 
endoderm is formed by cells springing from the flattened pole of the 
blastoderm, which rapidly multiply by fission. The mother-cells of 
the mesoderm remain in their original position, while the daughter- 
cells, as amoeboid bodies, or motile cells, move about in the yelk, till 
at last the segmentary cavity (Furchingshéhle) appears like a loose 
ageregate of stellate cells.” The author describes the formation of 
what he terms the primitive intestine (Urdarm) (which begins with 
an unfolding of the aboral pole), the commencement of the water- 
vascular system, and other matters which could not be explained 
without translating his paper in full. 
The Structure of the Common Mushroom.—This has been explained 
very fully by Mr. Worthington Smith, F.L.S., in a paper which he 
read before the Cryptogamic Society of Scotland (September 26), 
and which was illustrated by numerous drawings. He says “ that the 
entire substance of the common mushroom is made up of excessively 
small bladder-like cells ; these cells are so small in size and light of 
weight, that no less than 1,500,000,000,000 (one and a half billion) of 
cells go to every ounce of the mushroom’s weight. Mushrooms are 
generally grown by dealers from spawn or mycelium; this spawn is 
nothing but living matted cells in a resting condition, needing warmth, 
moisture, and darkness only for vivification. Mushrooms may, how- 
ever, be grown from the purple-black dust which falls from their 
