The influence of external conditions upon the growth and development of plants and animals has been known for a very long time, and has been made the subject of careful observation by many horticulturists and breeders, in addition to those who have attacked the problem in a more scientific spirit. As a rule, the changed conditions of environment, of which the effects were to be observed, were very considerable, and not such as might occur in nature, and the effects produced were not generally subjected to exact measurement. It seemed of interest, therefore, to determine as exactly as possible by measurement the effects which such slight changes in environment, as might occur under natural conditions, would produce in the growth of some organism, with a view to ascertaining how far the variations in size and relation of parts which occur in all animals may be caused by these external conditions, apart from such variations which arise from intrinsic differences in the germ. The animal chosen lor this purpose was the larva or pluteus of the sea-urchin, StroJigylocentrotus lividus. These larvae have the merit of being very hardy, and they develop readily from artificial fertilisations without any special precautions being taken. Moreover, it was found that these artificial fertilisations could be effected at all times of the year, irrespective of season. The chief objection to the choice of this animal lies in the fact that the growth of the larvae cannot be carried to the adult stage, so that it is only possible to measure the effect of environment at a particular period in their development. The plan of operations was very simple. About six or eight sea-urchins, which, as a rule, had been freshly obtained the same morning, were cut open, and pieces of the ovaries of each of the three or four female specimens shaken with forceps in a small jar of sea-water. Pieces of the testes were shaken in another jar, and the contents of the two jars mixed and stirred, the temperature being meanwhile noted. After standing an hour portions of this water containing the artificially fertilised ova were poured into glass jars containing 2 to 31/2 litres of sea-water. These jars were then transferred to a large glass tank, through which a stream of sea-water circulated, and were allowed to remain there throughout the whole period of development. Evaporation was prevented by covering the jars with glass lids. As a rule, the development was allowed to proceed for eight days, as the arms of the plutei attain their maximum development by the end of this time. A volume of saturated corrosive sublimate solution was then poured in each jar, such that the water should contain about '25 per cent, of it. In a few minutes all the larvae had sunk to the bottom. The supernatant liquid was poured off, and the larvae with 100 or 200 cub. centims. of water transferred to a small beaker, from which more of the liquid was poured off. The larvae were then washed in distilled water, and then in 50 percent, alcohol. They were finally transferred to, and preserved in, 70 percent, alcohol, to measure the larvae, they were washed on the slide in water, and mounted in glycerine. Several hundred, in positions suitable for measurement, could be obtained on a single slide. The larvae were measured under the microscope with a micrometer eyepiece, Zeiss, Obj. CC. Ocular, No. 3, The position of each larva measured was observed on the mechanical stage, and noted, so that it could not by mistake be measured twice. Three measurements were made, namely, the body length AB, the aboral arm length AC, and the oral arm length AD. The length of the calcareous skeleton in the body and limbs was always measured, in preference to the soft tissues surrounding it, as it is sharply defined, and therefore more suitable for the purpose. If is moreover of practically the same length as the soft tissues. In Fig. 1 are shown the measurements made. Only larvae in the position indicated in this figure were measured, as with larvae in the position indicated in Fig. 2, the oral arm is foreshortened.
Freezing avoidance and the distribution of antifreeze glycopeptides in body fluids and tissues of Antarctic fish