^-^ PRESIDENTIAL ADDRESS. 731 



to be fundamental respects. And, vice versa, we require the liberty to regard two 

 species as widely separated from eacb other in the system, even though they 

 possess identical types of avicularia. 



There are other questions which might have been considered in the Cheilo- 

 stomata, and, in particular, the presence or absence of oral or marginal spines and 

 the forms and distribution of the ovicells. The occurrence of the latter is, how- 

 ever, probably connected with the presence in the young zocecium of tissue which . 

 will give rise to an ovary ; and this implies the consideration of another factor 

 which is very difficult to estimate. 



I must not conclude without at sny rate referring to the fact that the Polyzoa 

 are by no means the only animals in which dimorphism or polymorphism occurs 

 as the result of blastogenic processes. But among the Coelenterates, for in- 

 stance, the occurrence of medusoid individuals cannot be considered apart from the 

 question of the sexual cells. There is, however, one series of cases among Hydroids 

 to which allusion may perhaps be made. I refer to the existence of pairs of 

 genera such as Corymorpha and Tubularia, Syncoryne and Coryne, Podocoryne 

 and Hydr actinia, in each of which pairs the two genera are distinguished by the 

 fact that one produces free medusae, while the other has sessile gonophores. There 

 is already some evidence that the validity of these generic distinctions is open to 

 question ; and the free medusoid individual and the sessile gonophore might con- 

 ceivably be related in such a way as to form members of an allelomorphic pair. 

 The same phylum contains another striking example of dimorphism in the distinc- 

 tion between gastrozooids and dactylozooids in many Hydroids; while in the 

 Siphonophora the differentiation of various forms of individual has advanced 

 much further. 



But I have already gone much beyond my evidence, and I must bring my 

 remarks to a conclusion by expressing the view that the causes which regulate the 

 differentiation of the individuals during the blastogenic development of the Polyzoa 

 are well worthy of further study, and that our knowledge of the unity of the vital 

 processes throughout the animal kingdom gives us reason to believe that they are 

 part of some general Biological law. 



The following Papers were then read : — 



1. The Migratory Movements of certain Shore-Birds as observed on the 

 Dublin Coast. By C. J. Patten, Sc.D. 



While the majority of my observations, extending over twenty years, on the 

 migratory movements of shore-birds along the Dublin coast have been incor- 

 porated in my work entitled ' The Aquatic Birds of Great Britain and Ireland,' 

 published at the end of the year 1906, I still continue to visit my former 

 hunting-grounds, and, with the aid of trustworthy correspondents, have col- 

 lected further information on the subject. To add to my personal observations 

 and to enable me to bring before this meeting of the British Association informa- 

 tion as recent as possible, I selected the Dublin coast this autumn as a seaside 

 resort. I would refer particularly to the Sanderling {Calidris arenaria). There is 

 now strong evidence to show that this bird is found in adult plumage throughout 

 the breeding-season on that coast. The observations of Mr, A. Williams, made 

 in July 1906 in this locality, on the Sanderling are of interest, as there was an 

 unusually large gathering of adult birds recorded. In many ways tlie Turnstone 

 repeats the migratory movements of the Sanderling, and is found throughout 

 the year on the Dublin coast in adult plumage. I have, moreover, dissected the 

 genitals of the female bird, shot at the height of the breeding-season, and have 

 found quite ripe ova. The time will, I believe, yet come when this species will 

 be discovered breeding on the Irish seaboard, or perhaps along the shores of 

 inland lakes. The movements of the Little Stint are most irregular ; a few pairs 

 appear during some autumn seasons, but in 1902 I have records of flocks from 

 the locality in question. The tameness of certain shore-birds on their first arrival 



