THE LAW OF LIKEXESS, AXD ITS WORKING. 211 



urchins, and their neighbours, the egg gives origin to a free- 

 swimming, active body, which develops a structure of its 

 own, and appears in a fair way to become, as might be 

 expected, the future star-fish. But within the body of this 

 first embryo another formation is seen to take place ; and 

 sooner or later this secondary development comes to assume 

 priority, and appears as the true and veritable representative 

 of the young star-fish, the primitive body or embryo which 

 produced it, being either absorbed into its substance or cast 

 off on development being fully attained and completed. 

 The production of the second star-fish, as it were, out of a 

 first-formed embryo, is paralleled by the curious case of a 

 certain kind of gall-flies (Ceadomyia), within the larvae or 

 caterpillars of which other young or larvae are produced. 

 The latter case partakes thus of the nature of a striking 

 exception to the ordinary laws of development, seeing that a 

 young and immature form possesses the power of producing 

 other beings, immature like itself, no doubt, but capable of 

 ultimate development into true flies. In other words, 

 heredity, or the power of like producing like, which ordinary 

 observation demonstrates to occur usually in the mature and 

 adult being, is here witnessed occurring in the young and 

 imperfect form. 



Certain very typical, but more complicated, cases of 

 animal development than the preceding instances are wit- 

 nessed in the reproduction of those curious animal colonies 

 collectively named "zoophytes." Any common zoophyte, 

 such as we may find cast up on our coasts or growing 

 attached to the fronds of tangle, is found to consist of a 

 plant-like organism (Fig. 29), which, however, instead of 

 leaves or flowers, bears numerous little animals of similar 

 kind, connected together so as to form a veritable colony. 

 Each of the little members of this colony possesses a mouth, 

 surrounded by arms or tentacles, and a little body-cavity in 

 which food is digested; and it may be noted that each 

 member of the colony contributes to form the store of 

 nourishment on which all the members, including itself, in 



