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or primary individual, does not show all the characteristics of the mature colony, 

 we must, however, assume that the determinants present in it do not find their 

 full expression until the buddinpr process has commenced. 



But we are by no means at the end of our difficulties, even in considering the 

 distribution of the appendages we have so far discussed. The instances already 

 given have for the most part been cases in which an entire colony differs in certain 

 respects from other colonies. We have still to notice the common case in which 

 there are differences in different parts of one and the same colony. No theory 

 can be considered complete unless it is able to account for these differences. 



I approach this part of the subject with great trepidation, conscious as I am of 

 the absence of experimental evidence for the suggestion I wish to make This 

 suggestion is, briefly, that if a segregation of characters normally takes place in tho 

 formation of the gametes of an organism, it is conceivable that an analogous 

 segregation may occur in the blastogenic processes, or, in other words, in the 

 formation of a bud. It may be asserted positively that there is a very definite 

 differentiation of individuals at this time, not only in the Polyzoa, but also in 

 other animals which increase by budding. The fact that some of these differen- 

 tiations appear to be alternative suggests the possibility that they are duo to a pro- 

 cess which resembles the Mendelian segregation of determinants in the gametes. 



One of the instances which appears to me specially suggestive in this con- 

 nection is the genus Steganoporelln, the species of which are remarkable for tho 

 dimorphism of their zooecia. This dimorphism is expressed, as we have already 

 seen, by differences in the opercula and in their muscles, and in the form of the 

 orifices which are closed by the opercula. It is not too much to say that every 

 individual in a Steganoporella colony belongs to one of the two types in question ; 

 and, so far as I am aware, intermediate forms of zooecium do not occur. It is thus 

 a positive fact that the blastogenic tissues undergo some sort of diflerentiation of 

 an alternative character, and there is at present no reason for believing that the 

 differentiation is in any way correlated with the production of sexual cells by 

 either of the two kinds of zocecia. 



Another case which seems to me specially suggestive is that of the simulta- 

 neous occurrence in the same colony of two different kinds of aviculavia. These 

 instances are not confined to a few species, but may be found in a number of 

 genera which do not constitute a single assemblage of related forms. The pointed 

 and rounded adventitious avicularia may be scattered about promiscuously in the 

 same colony, or even on the same zocecium. Sometimes avicularia of one of the 

 two types normally occur in a particular position, but are occasionally replaced 

 by avicularia of the other kind, an example of a general phenomenon to which 

 Professor Bateson has given the name of ' homojosis.' 



Excellent illustrations of this substitution may be taken from the genus 

 Setepora. In the JR. monilifera series already considered the munita and 

 acutirostris types of avicularia may occur in different fenestras of the same 

 colony. R. granulata usually possesses a labial avicularium and a frontal 

 avicularium, both of the small rounded kind. In one of the colonies of this 

 'species dredged by the 'Siboga' most of the labial avicularia are of this type, but 

 a certain proportion of the zocecia have a pointed labial avicularium. In another 

 colony most of the frontal avicularia are small and round, but in some of the 

 zooecia they are large and pointed. In both instances the examination of 

 the mandibles proved the reality of the distinction inferred from the shape of the 

 calcareous parts. 



Instances of a similar substitution could easily be multiplied, while the cases 

 of the simultaneous occurrence of the two kinds of adventitious avicularia are 

 innumerable. Without going so far as to say that intermediate conditions do not 

 occur — a generalisation that could only be established by very prolonged study — 

 it may certainly be maintained that it is the general rule for an avicularium to 

 assume one of the two types. In a suitable preparation it is usually quite easy 

 to sort all the mandibles into their proper group at first sight, and without having 

 to pause to consider doubtful cases. This fact is surely significant, and it can 

 at least be argued that in the blastogenic processes by which the avicularia have 



