ZooL— Vol. III.] B A NCR0F7— COMPOUND ASCIDIANS. 179 



of the systems, or determining that part of the composite 

 colony would behave differently so far as fusion is concerned 

 toward a third colony from what it did before it became a 

 part of the composite colony, are such difficult questions 

 that a more extended series of observations would be needed 

 to answer them. 



But although these characters appear to be the same 

 throughout the whole extent of the colony on account of 

 the common origin of the whole from a single larva, it does 

 not necessarily follow that so far as these characters are 

 concerned the colony is merely the sum of its component 

 zooids. It is only in the case of characters associated 

 solely with the zooids that this conclusion may be drawn. 

 Thus it is evident in the case of the fourth morphological 

 character, that the colony possesses zooids of a constant 

 color, because all the zooids have the same color, and that 

 hence, in this respect, the colony is merely the sum of its 

 zooids. The same may be said of the fourth physiological 

 character, the force causing the short life of the zooids; 

 and to a certain extent of the second physiological charac- 

 ter, the system-forming force, though in this case the con- 

 stant size of the systems may possibly be partially due to 

 something outside of the zooids, such as some specific 

 chemical substance in the test. 



The first physiological character — the quality which 

 determines fusion — probably does not depend upon anything 

 resident within the zooids, but is concerned with the test 

 and the blood-vessels; for, as we have seen, the initial step 

 of the fusion depends only upon these two parts of the 

 colony. But so little is known about this character, and in 

 fact about the second and fourth physiological characters 

 as well, that nothing definite can be said about the parts of 

 the colony in which they reside. 



To sum up, then, it is seen that, of the eight characters 

 determining the individuality of the colony as a whole, five 

 are not intimately associated with the zooids, and hence 

 cannot be considered as the sum of the characters resident 

 in the zooids; these are: — 



