168 
PROGRESS OF MICROSCOPICAL SCIENCE. 
To these pages we would commend all who desire to know something 
of our recent knowledge of these important groups of animals. We 
can only state the results arrived at, which are as follow in the case 
of the Infusoria. The writer says : " There are, then, two modes of 
development among the Infusoria (Ciliata) : 1. By fission. 2. By pro- 
duction of internal ciliated embryo arising from eggs. We have, then, 
for the first time among the Protozoa, if the observations of Balbiani be 
correct (though this is denied by good observers), truly sexual animals, 
producing true eggs and spermatic particles. The same animal repro- 
duces both by fission and by the production of ciliated embryos. Most 
of them before producing embryos imdergo fission. This is comparable 
to the alternation of generations among the Hydroids, Aphides, &c." 
In the same manner he gives the following summing up as regards the 
stages of the life-history of sponges : 1. Fertilization of a true egg by 
genuine spermatozoa ; both eggs and sperm-cells arising from the 
inner germ-layer. 2. Total segmentation of the yolk, or proto- 
plasmic contents of the egg. 3. A ciliated embryo. 4. A free-swim- 
ming " planula "-like larva, with two germ-layers, not, however, 
originating as in the true planula of the acalephs. The planula 
becomes sessile, spicules are developed in the hinder end of the body, 
afterwards a gastro-vascular cavity appears, constituting the— 5. Gas- 
trula stage. 6. A mouth and side openings appear and the true sponge 
characters are assumed. 
The Power of Motion which Diatoms possess. — In a recent paper 
before the Academy of Natural Science of Philadelphia ( ' Proceedings,' 
p. 113), Professor Leidy made some remarks on the moving power of 
Diatoms, Desmids, and other Algae. While the cause of motion re- 
mains unknown, some of the uses are obvious. The power is con- 
siderable, and enables these minute organisms, when mingled with 
mud, readily to extricate themselves and rise to the surface, where they 
may receive the influence of light and air. In examining the surface 
mud of a shallow rain-water pool in a recent excavation in brick-clay, 
he found little else but an abundance of minute diatoms. He was not 
sufficiently familiar with the diatoms to name the species, but it 
resembled Navicula radiosa. The little diatoms were very active, 
gliding hither and thither, and knocking the quartz sand grains about. 
Noticing the latter, he made some comparative measurements, and 
found that the Naviculse would move grains of sand as much as 
twenty-five times their own superficial area, and probably fifty times 
their own bulk and weight, or perhaps more. 
How Pigment-cells are influenced hy the N.erves. — We are glad to 
see that M. Pouchet, who published one of his first papers on the sub- 
ject in these pages, has been awarded the Montyon prize by the 
French Academy for his researches. The following abstract of the 
Commission's report appears in the 'Medical Eecord,' Jan. 13, 1875 : 
The memoir is in two parts, one purely anatomical, the other 
physiological. The former contains new facts, but it is the latter 
that has chiefly engaged the attention of the Commission. 
From this point of view the work is almost without precedent. 
