A long series of experiments was made on Amblyopsis and Chologaster to determine their reaction to white and monochromatic light. Without going into the details of these experiments, it may be stated that Amblyopsis avoids the light, regardless of the direction or the color of the rays. The same is true of Chologaster, except that they were positively attracted by the red rays of the spectrum as against the blue. We owe the first observations on the breeding habits of Amblyopsis to Thompson, who states that a fish “was put in water as soon as captured, where it gave birth to nearly twenty young, which swam about for some time, but soon died; ... they were each four lines in length.” Little or nothing has been added to our knowledge of this subject since that time, but the highly interesting supposition of Thompson that they were viviparous has gained currency, and it is therefore unfortunate that in this respect he was in error. Putnam adds to the above that, judging from some data in his possession, the young are born in September and October, and further along remarks that they are “undoubtedly” viviparous. The eggs are laid by the female in under her gill membrane. Here they remain for perhaps two months, till the yolk is nearly all absorbed. If a female with young in her gill pouches is handled, some of the young are sure to escape. This was observed, and gave rise to the idea that this fish is viviparous. Eggs have been obtained as early as March 11th and as late as September, and the indications are that the breeding season extends throughout the year. The eggs are large--2.3 millimetres in diameter from membrane to membrane--and about sixty to seventy are laid at one time. Certain structures gain an entirely new significance in the light of the breeding habits. These are the enlarged gill cavities, with the small gills, the closely applied branchiostegal membrane, and the position of the anus and sexual orifices. The latter are placed just behind the gill membrane in such close proximity to it that they can be covered by it. It is probable, therefore, that the membrane is drawn over the sexual orifice and the eggs deposited directly into the gill cavity. In an individual thirty-five millimetres long the anus is situated between the origin of the pectorals; in one twenty-five millimetres long it lies between the pectorals and ventrals. In the young it lies behind the ventrals, as in other fishes. [Illustration: FIG. 16.--The embryo of _Typhlogobius_, showing the well-developed eye. FIG. 17.--A young _Typhlogobius_, times 4-2/9. FIG. 18.--Adult _Typhlogobius_. FIG. 19.--Adult _Gillichthys-y-cauda_ living in crab holes in San Diego Bay. FIG. 20.--Young _Gillichthys mirabilis_ under the same magnification as Fig. 17.]