314 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 
405. Yellow sponges of various kinds, artificially bleached. 
406. Sheepswool sponges, artificially bleached. 
407. Samples: 
Sponges in condition in which they are landed and sold by the fishermen, pre- 
sented by Mr. John K. Cheney, Tarpon Springs, Fla. 
DEVELOPMENT OF A TROUT. 
408. Models illustrating the early stages of development of a trout: 
The fertilized egg is shown in model 1. The white portion represents the disk of 
protoplasm which by its growth and development gives rise to the embryo. The 
yellow portion, which is relatively large in the early stages, is the yolk, which serves 
as food and is gradually absorbed during the process of development. The first 
marked change is the formation of a furrow which divides the protoplasm into two 
masses or blastomeres, as shown in model 2. Each of these becomes divided by a 
cross furrow, producing 4 cells, as shown in model 3, and subsequent divisions give 
rise to 8, 16, 32, and eventually numerous cells, as shown in models 4-8. During 
the later ‘stages of this process the protoplasmic matter has increased by the absorp- 
tion of some of the yolk, which becomes thereby relatively and actually smaller. 
The mass of cells has become lens-shaped, its lower surface dipping somewhat into 
the yolk, as shown in models 9 and 10, which represent sections of about the stages 
shown in models 6 and 7, respectively. 
The mass of cells which has before been uniform now becomes differentiated into 
two layers, and a cayity appears between the lower layer and the yolk. This is 
shown in models 11 and 12, where the layers are indicated by conventional colors. 
Soon after, a third layer appears between these two, as shown in model 13. These 
three layers give rise to all the tissues of the adult fish, in general terms, the outer 
giving rise to the outer skin, brain, and sense organs, the inner or lower layer to the 
lining of the alimentary canal and to parts of the related organs, and the middle 
layer to the bones, muscles, blood vessels, etc. 
As the protoplasmic portion or blastodermic disk gradually extends over the yolk 
its edge becomes thickened and the body of the fish begins as a tongue-like growth 
inward from a part of this ring, gradually extending over the disk, as shown in 
models 14-21. The thickened folds shown in model 21, and several of its predeces- 
sors, represent the developing brain and spinal cord. 
Subsequently the sense organs, alimentary canal, and other organs appear, the 
head and tail of the embryo grow free from the now inclosed dwindling yolk, and 
at the time of hatching the latter remains as a protuberant sac on the fish’s belly, 
furnishing nourishment to the fry until such time as it is able to take food through 
its mouth. 
BacreriAL EXuisir. 
409. Cultures of bacteria which infest fishes or are found in the water: 
The exhibit of bacteria is designed to illustrate the Commission’s work in a com- 
paratively new field. Bacteria are of chief importance in human disease, and it was 
to be anticipated that they would play a corresponding part in lower forms. Some 
important affections of fishes have been traced to bacterial infection, and several 
of the cultures shown were made from the blood or tissues of diseased fishes. Notable 
among these is the bacillus of tuberculosis in fishes, from a European source, this 
disease not havi ing yet appeared among fishes in this country. The principal pus 
coce i are also represented, among whic h the streptococcus is most important, causing 
the ‘‘oyster hand,’’ familiar in oyster regions, and arising from wounds caused by 
“ shucking’’ oysters or handling the shells. 
A number of salt and fresh water bacteria}are shown, including some handsome 
chromogens. Some of these are also frequently found unassociated with water. The 
phosphorescent organism exhibited produces phosphorescence in the sea, and will 
grow on cooked fish, producing a readily appreciable amount of light. The com- 
moner water organisms may be frequently obtained from tissues or regions of fishes 
to which they have access. 
A few cultures are included which have been grown from fishes to all appearances 
free from disease. These are bacilli and were obtained from the blood and from the 
peritoneal cavity of brook trout. They represent normal bacteriology of fishes, a 
new and little known field of rather uncertain significance, but suggestive and full of 
interest as indicating possible important relations to normal life processes. 
The cultures, as exhibited, are not living, the growth having been killed and the 
medium upon which it rests ‘hardened by formalin. 
