Several attempts have been made at different times to connect the facts in regard to the extrusion of the polar bodies with those involved in the determination of sex. Minot suggested, in 1877, that the egg ejects by means of the polar bodies its male elements, which are again received in the fertilization of the egg by the spermatozoon. The same idea has also been expressed by others. It has been objected to this view that one polar body ought to suffice, and that no similar throwing out of part of its substance is found in the process of formation of the spermatozoon, which should, on the hypothesis, throw out its female elements. It would seem, on first thought, that this view might find support in the idea expressed above, namely, that in one of the polar bodies half of the chromosomes pass out, so that there is conceivably a separation of the maternal from the paternal. If this were the case also in the spermatozoa, then two of each four would be paternal and two maternal. This is, however, a very different thing from supposing them to be male and female, for it by no means follows, because the chromosomes correspond to those of the father or of the mother in the sum of their characters, that they are, therefore, also male or female in regard to sex. It has been pointed out already, that in most parthenogenetic eggs only one polar body is extruded. There are, it is true, a few apparent exceptions to this rule, but in most cases it is certain that only one is extruded. In several cases the beginning of the formation of the second maturation division of the nucleus takes place, but after the chromosomes have divided they come together again in the nucleus. If each polar body be interpreted as equivalent to a spermatozoon, then this result is rather a process of self-fertilization than true parthenogenesis. It is, nevertheless, true that in some cases development seems to go on after both polar bodies have been extruded. Moreover, it has been found possible to cause the eggs of the sea-urchin to begin their development by artificial solutions after they have extruded both polar bodies. A single spermatozoon may also produce an embryo if it enters a piece of egg-protoplasm without a nucleus. The last instance is a case of male parthenogenesis, and if the theory of the equivalency of spermatozoon and egg be correct, this is what should occur.