530 



NATURE 



[December 22, 1921 



First, Dr. Bather quotes an observation of Dr. 

 Mortensen's in which he describes the larva of an 

 Ophiurid dropping the young brittle-star and then 

 proceeding to regenerate itself, and states that this 

 observation suggests that the metamorphosis of 

 Echinoderms is an alternation of generations. I can 

 only say that this observation of Dr. Mortensen stands 

 in urgent need of confirmation, and that it is totally 

 opposed to what we know of the normal development 

 of Ophiurids. In the development of Ophiothrix 

 fragilis the adult takes over from the larva the mouth, 

 oesophagus, stomach, intestine, peritoneal sacs, and 

 aboral integument, and what is left of the larva after 

 this abstraction is merely the ciliated band, the larval 

 organ of locomotion. This development is no more 

 an alternation of generations than is the development 

 of the veliger into the adult mollusc. The same type 

 of metamorphosis is found in the pelagic larvae of 

 Holothuroids and Echinoids ; in Asteroids the only 

 additional feature to be observed is the shrivelling 

 and disappearance of the praeoral lobe which acts as 

 stalk during the earlier stages of metamorphosis. 

 Secondly, Dr. Bather states that Dr. Mortensen has 

 shown that the Brachiolaria stage in Asteroid 

 development (in which the larva uses its praeoral lobe 

 as a stalk) cannot be homologous with the similar 

 stage of development in Crinoids, since it is found only 

 amongst the "more specialised forms of Asteroids." 



No more rash statement could be made nor one 

 rnore devoid of foundation. Modern Asteroids are 

 divided into five groups, viz. Forcipulata, Valvata, 

 Velata, Paxillosa, and Spinulosa. Nothing whatever 

 is known of the development of any valvate and velate 

 form, but the fixed stage is found not only in the 

 development'of the Forcipulata (which Dr. Mortensen 

 arbitrarily regards as the most specialised forms), 

 but also in the development of the Spinulosa (which 

 ail admit to be the most primitive group). In the 

 Paxillosa, which include the British genera Astro- 

 pecten and Luidia, and which, mirabile dictu, Dr. 

 Mortensen appears to regard as primitive forms, the 

 fixed stage is omitted ; the larva apparently amputates 

 its praeoral^ lobe and does not use it as a stalk. 



The Paxillosa, so far from being primitive, are quite 

 a modern development of Asteroid structure in the 

 Ophiuroid direction. They have in most cases lost 

 the anus and in all cases the sucking discs of the tube 

 feet,_ and they have developed a quite un-Asteroid 

 mobility and muscularity of the arms. Luidia even 

 snaps off the arms on irritation exactly like an 

 Ophiuroid. 



The reason why the fixed stage is omitted in their 

 development is not far to seek. What we know of 

 their habits points to their being inhabitants of the 

 sand and mud. Such a habitat is utterly unsuitable 

 for the support of a fixed stage, and consequentlv this 

 stage has been omitted in their life-historv. 



When,_ however, we reflect that the Echinoderms 

 are admitted by all to be descended from the same 

 stock, that this stock must have passed through a fixed 

 stage, since primitive Crinoids are fixed, and that the 

 stalks of Crinoids and Asteroids are formed from the 

 same region of the larva, we shall be in a position to 

 estimate the value of Dr. Mortensen's views. His 

 ideas of^ the ancestry of Echinoderms would carry 

 more weight if he had worked out with thoroughness 

 the complete life-history of any Echinoderm. 



Lastly, I should like to protest against the idea that 

 those interested in Echinoderms agree with the over- 

 estimate of the importance of trifling oeculiarities in 

 the structure of pedicellariae in which Dr. Mortensen 

 indulges. As Dr. Bather savs, thev are of no use to 

 the palaeontologist, and Dr. Bather,' who is not onlv a 

 systematist, but also a first-class morphologist, will 

 NO. 2721, VOL. I08I 



realise that Dr. Mortensen's views are accepted by few 

 except himself. E. W. MacBride. 



Royal College of Science, South Kensington, 

 London, S.W.y, December 14. 



Prof. MacBride has allowed his enthusiasm for the 

 truth, as he sees it, to blind his eyes to what I actually 

 did say. I said the idea of alternation of generations, 

 though recalled by Dr. Mortensen's account of an 

 observation, was "not really justified." I also charac- 

 terised Dr. Mortensen's own inference from that ob- 

 servation as "audacious." I am glad to find that 

 Prof. MacBride agrees with me, even if his mode of 

 expressing agreement be unusual. 



I did not say that Dr. Mortensen had "shown" 

 (which I take to mean "proved") those statements 

 and conclusions concerning the Brachiolaria and its 

 sucking disc to which Prof. MacBride takes exception. 

 By using the expression "none the less " I meant to 

 imply that his conclusion on this point was not on all- 

 fours with his general conclusion. Prof. MacBride 

 differs from me in the vigour with which he rubs in 

 that argument. I am glad that my remark has 

 aroused so doughty a champion to the defence of the 

 Brachiolaria, but I confess that I am not as yet pre- 

 pared to broider any published classification of the 

 Asteroidea on my own banner. 



It is not for me to break any lances in defence of 

 Dr. Mortensen, but if Prof. MacBride is acquainted 

 with Dr. Mortensen's "Studies in the Development of 

 Crinoids" (see Nature, vol. 107, p. 132, March 31, 

 192 1) I am rather astonished that he should so belittle 

 our Danish colleague's work on those lines. As for 

 the importance that Dr. Mortensen attaches to pedi- 

 cellariae, I incline to think that it is his critics who 

 "overestimate" it. He himself has written (1907, 

 "Ingolf Exped., Echinoidea," vol. 2, p. 12) :— " I have 

 never stated that the classification has always to be 

 based on the pedicellariae as the most important factor; 

 on the contrary, I am of opinion that where structural 

 characters of some significance occur in the test, these 

 are, upon the whole, of higher classificatory value than 

 the characters in the pedicellariae." 



Prof. MacBride is as friendly and complimentary to 

 me as he always is, even when we differ, but, however 

 much he may differ from Dr. Mortensen, I do hope 

 he realises that the latter has furnished us in this 

 memoir with a number of novel observations obtained 

 with labour and recorded with skill. 



F. A. Bather. 



Some Problems in Evolution. 



The address of Prof. Goodrich on " Some Problems 

 in Evolution," which I read in Nature of 

 November 24, incidentally deals in a slight but some- 

 what dogmatic manner with the question, "What 

 share has the mind taken in evolution? " I do not 

 propose mvself to attempt to answer this question, 

 but onlv to point out that the grounds on which 

 Prof. Goodrich deals with the matter are quite incon- 

 sistent with w^ell-established phenomena which are 

 familiar to psvchologists and psychotherapists. 



Prof. Goodrich savs, "I would maintain that 

 there is no justification for the belief that it (mind) 

 has acted, or could act, as something guiding or 

 interfering w^Ith the course of metabolism." He 

 scouts the idea "of the influence of the mind on the 

 activities of the bodv," and says, "we cannot con- 

 ceive how a physical process can be interrupted or 

 supplemented bv non-phvsical agencies." He tells us 

 that the student of blologv "should realise that the 

 mental series of events lies outside the sphere of 

 natural science," and relegates such matters to the 

 realm of philosophy. 



