EVIDENCE FROM COLONIAL OR COMPOUND ANIMALS. 283 



zoophyte-units wither, fall, and in like fashion are represented anew 

 in the constitution of the organism. Then, lastly, the origin of the 

 zoophyte in an egg is worthy of note. Each zoophyte originally 

 springs from an egg, which, passing through the changes common to 

 the early development of all ova, produces an embryo which settles 

 down and attaches itself to some fixed object. 



This first embryo next assumes the likeness of a single little 

 hydra-like unit of the zoophyte colony. Then the process of bud- 

 ding commences. Bud after bud is produced, each growing into the 

 likeness of the primary one, and all adhering together as parts of a 

 connected organism, until we find reproduced before our eyes the 

 tree-like form with which our research began. Thus a hydra and a 

 zoophyte are very nearly allied ; the chief difference between these 

 organisms consisting in the fact that, whilst the buds remain perma- 

 nently connected together in the latter, they are intended to seek an 

 independent existence in the former. True, there are buds produced 

 by the zoophyte which in many cases detach themselves and swim 

 freely in the sea under the guise of " jelly-fishes," and which, apart 

 from the zoophyte, mature the eggs from which new generations of 

 these plant-like animals will spring. But these floating jelly-fishes, 

 despite their freedom, are in reality buds of the zoophyte. They 

 are connected by all the ties of blood-relationship with their plant- 

 like parent, and are essential parts of the zoophyte-colony even 

 when separated from the parent-organisms by many leagues of sea. 



In all zoophytes the component units of the colony belong to one 

 type. Whatever their function, they are modelled on the type of the 

 hydra, and on that of the ordinary nutritive members of these animal 

 trees. Even the jelly-fish buds just mentioned, are but modifications 

 of the hydra type. This interesting and important feature in their 

 history is proved by the fact that, when their generative functions 

 have been discharged, they may revert to the form of the nutritive 

 members of the colony. We know, lastly, of cases in which a 

 zoophyte-colony may number no fewer than seven apparently dif- 

 ferent kinds of members; these units, notwithstanding the diverse 

 functions they perform, exhibiting a fundamental agreement in type 

 and structure. There is seen, therefore, a close parallelism between 

 the repetition and modification of parts in the colonial zoophytes^ 

 and the vegetative repetition of the leaves and buds of the tree. 



The Flustras, or "Sea-mats " (Fig. 190), illustrate a slightly different 

 phase of colonial relationship in animals from that presented by the 

 zoophytes. We have seen that each member of the zoophyte-colony 

 exists in intimate structural relationship and connection with every 

 other unit of the compound organism. But in the " Sea-mats " each 

 of which presents us with the appearance of a piece of pale brown 

 seaweed, bearing on either side its hundreds of little cells (Fig. 190, b\ 



