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THE POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



embryo, is paralleled by the curious case of a i 

 certain kind of gall-flies (Cccidomyia), within the 

 larvae or caterpillars of which other young or 

 larvae are produced. The present case partakes 

 thus of the nature of a strikiug 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 occur- 

 ring in the young and imperfect form. 



Certain very typical but more complicated 

 cases of animal development than the preceding 

 instances are witnessed 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 con- 

 sist of a plant-like organism, which, however, 

 instead of leaves or flowers, bears numerous lit- 

 tle 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 turn 

 depend for sustenance. Such a veritable animal- 

 tree, growing rooted and fixed to some object, 

 increases by a veritable process of "budding." 

 As the animal-buds die and fall off, new buds 

 aie thrown out and developed to supply the 

 place of the lost members; the zoophyte, like 

 the tree, renewing its parts according to the 

 strict law of heredity, and each new member of 

 the colony bearing as close a likeness to the ex- 

 isting members as that borne by the one leaf 

 of a tree to its neighbor-leaves. But, as the 

 tree sooner or later produces flowers which are 

 destined to furnish the seeds from which new 

 trees may spring, so the zoophyte in due time 

 produces animal-buds of a kind differing widely 

 from the ordinary units which enter into its 

 composition. These varying buds, in very many 

 cases, appear in the likeness of bell-shaped or- 

 ganisms, and, when they detach themselves from 

 the zoophyte-tree and swim freely in the sur- 

 rounding water, we recognize in each wandering 

 bud a strange likeness to the familiar Medusae 

 or jelly-fishes, which swarm in the summer seas 

 around our coasts. Living thus apart from the 



zoophyte-parent, these medusa-buds may pass 

 weeks or months in an independent existence. 

 Ultimately, however, they develop eggs, and with 

 the production of the eggs the clear, elegant, 

 glassy bodies undergo dissolution, and vanish 

 away amid the waters, to which, in the delicacy 

 of their structure, they presented so close a re- 

 semblance. From each egg of the jelly-fish-bud 

 there is gradually developed, not a medusa, but 

 a zoophyte. The egg, in fact, develops a single 

 bud of the zoophyte, and this primitive bud, by 

 a process of continuous budding, at last produces 

 the connected, tree-like form with which the life- 

 history began. Thus the zoophyte is seen to give 

 origin to a jelly-fish, and the jelly-fish in turn re- 

 produces the form of the zoophyte — one genera- 

 tion of animals, as the older naturalists believed, 

 " alternating " in this way with another. 



The law of likeness would at first sight seem 

 to be ill-adapted, in virtue of its essential nature, 

 to explain the cause of an animal, such as the 

 zoophyte, producing an entirely different being, 

 represented in the present instance by the jelly- 

 fish-bud ; and it might appear to be equally inex- 

 plicable that the progeny of the jelly-fish should 

 revert to the zoophyte stock and likeness. The 

 case of those curious oceanic organisms, allied to 

 the " sea-squirts," and known as Salpce, presented 

 to the zoologists of former years phenomena of 

 an equally abstruse kind. The salpae are met 

 with floating on the surface of the ocean in two 

 distinct forms. One form exists in the shape of 

 a long, connected " chain " of individuals, while 

 the other form is represented by single salpae. 

 It was, however, ascertained that these two va- 

 rieties were linked together in a singularly inti- 

 mate manner by their development. The chain- 

 salpae were found to produce each a single egg, 

 which developed into a single salpa ; and the 

 latter, conversely, produced each a long " chain " 

 of individuals — the one variety, in fact, repro- 

 ducing the other. The apparently mutual devel- 

 opment of the zoophyte and the jelly-fish, and of 

 the chain and single salpa, is, however, explica- 

 ble, as far as its exact nature goes, on other 

 grounds than those on which the naturalists of 

 former years accounted for the phenomena. The 

 jelly-fish is not ad istinct animal from the zoophyte, 

 but merely one of its modified buds, produced, 

 like the other parts of the animal-tree, by a pro- 

 cess of budding, and destined for a special end — 

 that of the development of eggs. The latter il- 

 lustrate the law of heredity because they are to 

 be regarded as having been essentially and truly 

 produced by the zoophyte, into the form of which 



