[Illustration: FIG. 45, Larva of Starfish (Bipinnaria), × 100 (after Müller). 46, Larva of Starfish (Bipinnaria), × 100, seen from the side—_a_, mouth; _b_, œsophagus; _c_, stomach; _c´_, intestine. 47, Larva of another Bipinnaria, showing the commencement of the Starfish—_g_, canal of the ciliated sac; _i_, rudiments of tentacles; _d_, ciliated band.] But while certain Starfishes thus go through metamorphoses similar in character, and not less remarkable than those of sea-eggs, there are others—as, for instance, the genus _Asteracanthion_—in which development may be said to be direct—the organs and appendages special to the Pseud-embryo being in abeyance; while in another genus, _Pteraster_, they are reduced to a mere investing membrane.[35] Among the Ophiurans also we find two well-marked types of development. Some passing through metamorphoses, while others, as for instance _Ophiopholis bellis_, “is developed very much after the method of _Asteracanthion Mülleri_, without passing through the Plutean stage.”[36] Even in the same species of Echinoderm the degree of development attained by the larva differs to a certain extent according to the temperature, the supply of food, &c. Thus in _Comatula_, specimens which are liberally supplied with sea-water, and kept warm, hurry as it were through their early stages, and the free larva becomes distorted by the growing Pentacrinus (see Fig. 43), almost before it has attained its perfect form. On the other hand, under less favourable conditions, if the temperature is low and food less abundant, the early stages are prolonged, the larva is longer lived, and reaches a much higher degree of independent development. Similar differences occur in the development of other animals, as for instance, in the Hydroids,[37] and among the insects themselves, in Flies;[38] and it is obvious that these facts throw much light on the nature and origin of the metamorphoses of insects, which subject we shall now proceed to consider. CHAPTER IV. _ON THE ORIGIN OF METAMORPHOSES._ The question still remains, Why do insects pass through metamorphoses? Messrs. Kirby and Spence tell us they “can only answer that such is the will of the Creator;”[39] this, however, is a general confession of faith, not an explanation of metamorphoses. So indeed they themselves appear to have felt; for they immediately proceed to make a suggestion. “Yet one reason,” they say, “for this conformation may be hazarded. A very important part assigned to insects in the economy of nature, as we shall hereafter show, is that of speedily removing superabundant and decaying animal and vegetable matter. For such agents an insatiable voracity is an indispensable qualification, and not less so unusual powers of multiplication. But these faculties are in a great degree incompatible; an insect occupied in the work of reproduction could not continue its voracious feeding. Its life, therefore, after leaving the egg, is divided into three stages.”