TRANSACTIONS OF SECTION D. 635 



Crustacea gigantostraca (to include the Eurypterida and Xiphosura) is the nearest 

 expression of the truth. It becomes thereby the more regrettable that in a recent 

 revision of the taxonomy of the Limuloids the generic name Carcinoscorpius 

 should have found a place. ^"* 



I foresee the objection that the antennifonn condition of the shorter limbs 

 may be secondary and due to change. There is no proof of this. Against it, it 

 may be said that the number of the segments is normal, and that where nature 

 effects such a change, elongation is with the multi-articulate state the only process 

 known; as, for example, with the second leg of the Phrynidse, the so-called 

 second pareiopod of the Polycarpidea, and the last abdominal appendage of 

 Apseudes}'''^ 



That advances such as we have now considered should lead to new departures 

 is a necessity of the case ; and it but remains for me to remind you that within 

 the last decade statistical and experimental methods have very properly come 

 more prominently into vogue, in the desire to solve the problems of variation 

 and heredity. Of the statistical method, by no means new, 1 have but time to 

 recall to you the Presidential Address of 1898 by my friend and predecessor in 

 this chair, himself a pioneer ; and of the experimental method I can but ciie an 

 example, and that a most satisfactory one, justifying our confidence and support. It 

 concerns the late Professor Milne-Edwards, who in 1864 described, from the Paris 

 Museum, the head of a rock lobster {Palinw-us penicillatus), having on the left 

 side an antenniform eye-stalk."'' With the perspicuity distinctive of his race, he 

 argued in favour of the 'fundamental similarity of parts susceptible to revert to 

 their opposite states.' The matter remained at this, till, on the removal of the 

 ophthalmite of certain Crustacea, it was found that in regeneration it assumeo a 

 uniramous multiarticulate form ; and it is an interesting circumstance that in 

 the common crayfish the biramous condition normal to the antennule may occur. 

 An example this of a fact which no other method could explain. ^"1 



When all is said and done, however, it is to the morphological method that I 

 would appeal as most reliable and sound. And when we find (i.) that in certain 

 Compound Tunicates the atrial wall, in the egg development delimited by a pair 

 of ectoblastic invaginations, in the bud development may be formed from the 

 parental endodermic branchial sac ; ^'^" (ii.) that regenerated organs are by no means 

 derivative of the blastemata whence they originally arose ; ^*^^ (iii.) that in the 

 development of a familiar starfish the inner cells of the earliest segmentation 

 stages, by intercalation among the outer, contribute half the fully formed blastula ; i*^* 

 (iv.) that there are Diptera in existence in which, while it is well-nigh impossible 

 to discriminate between the adult forms, there is reason to believe the pupa 

 cases are markedly and constantly distinct ; it becomes only too evident that 

 the later embryonic and adult states are those most reliable for all purposes of 

 comparison, and that it is by these that our animals can best be known and 

 judged. Caution is, however, necessary with senility and age, since certain 

 skiiUs have been found to assume at "this period characters and proportions 

 strikingly abnormal,^*^ and by virtue of a most important discovery, which we 

 owe to the Japanese, that in certain Holothurians, the calcareous skeletal deposits 

 may so change with age, as to render specific diagnoses based on their presumed 

 immutability invalid."'' Advance, real and progressive, is in no department of 

 zoological inquiry better marked than in comparative morphology, and it is for the 

 pre-eminence of this that I would plead. Educationally, it affords a mental 

 discipline second to none. 



We live by ideas, we advance by a knowledge of facts, content to discover the 

 meaning of phenomena, since the nature of things will be for ever beyond our 

 grasp. 



And now my task is done, except that I feel that we must not leave this place 

 without a word of sympathy and respect for the memory of one of its sons, an earnest 

 devotee to our cause. William Thompson, born in Belfast, 1806, became in due 

 time known as ' the father of Irish natural history.' By his writings on the Irish 

 fauna, and his numerous additions to its lists, he secured for himself a lasting 



