July 24, 1890] 



NATURE 



309 



or, differentiating with respect to r, 

 21-1 = - d{r''-p)ldr 



— - 2rp - r^dpldr, 

 or 



t = - p - \rdpldr. (28) 



(27) The first assumption of Barlow, that there is no cubical 

 compression, gives t ■= \p; and therefore 

 dplp + idrlr = o, 

 or 



pr^ = a, a constant, 



p = 2t = ar - ^. 

 Rankine's second assumption of uniform hydrostatic stress 

 gives t = - p; and therefore 



dp/dr = o, p = b, & constant. 

 Hence, in the general case, 



p = ar~^ + b, t = lar-^ - b; . . . . (29) 

 where a and b are determined from the given values/; and/^ of 

 the internal and external applied pressures ; so that 



pi = ari- 



b, Po 



A^ 



/<r,3 



(30) 



(28) We may now take \at — ^ - ^ to represent the longi- 

 tudinal tension at radius r in the cylindrical part of the closed 

 vessel. 



Unfortunately for the strict mathematical accuracy of this 

 method, we must suppose the circumferential tension to change 

 suddenly from its value given from the formula ar—- - b to 

 one given by a formula of the form la'r — ^ - b', in passing 

 from the cylindrical part to the hemispherical end. 



A. G. Greenhill. 

 (To be continued.) 



STUDIES IN BIOLOGY FOR NEW ZEALAND 

 STUDENTS.^ 



TT is now generally recognized that of all recent works dealing 

 •*■ with elementary natural science, none have more thoroughly 

 revolutionized our methods of teaching than those of Huxley, 

 well known ; and the years 1875-77 will be for all time memor- 

 able to English-speaking students, as those which marked their 

 publication. The principles therein laid down are now so well 

 known and generally adopted, that explanation of them would 

 be here superfluous. In his work on " Physiography" the 

 author points out (preface, p. viii.) that any intelligent teacher 

 will have no difficulty in making use of the resources of his 

 surroundings, in the manner and to the end laid down by him- 

 self ; and this, in the long run, is the refrain of the method by 

 which he has effected the revolution alluded to. So far as 

 external evidences go, this wise counsel appears to have been 

 nowhere more readily acted upon than in New Zealand. 



Prof. Hutton, now of Christchurch, New Zealand, early took 

 the hint ; and, in so doing, produced the first of the series of 

 pamphlets now under consideration. He chose for his purpose 

 the Shepherd's Purse (cf. Nature, vol. xxiv. p. 188), and Prof. 

 Parker, who succeeded him, has, in turn, prepared notes serial 

 with those of his predecessor — upon " The Bean Plant" (1881), 

 and now upon "The Skeleton of the New Zealand Crayfishes." 

 During the interval between the publication of Prof. Parker's 

 pamphlets there appeared the third of the series, entitled "The 

 Anatomy of the Common Mussels {Mytilus latus, eduHs, and 

 mageilanicus)." This, the work of Alex. Purdie, and the least 

 didactic of the series, was originally presented as a thesis for the 

 degree of M. A. in the University of New Zealand. 



The pamphlets alluded to are illustrated— in the case of that 

 before us, by six clear woodcuts ; and those of Parker, with 

 which we need now alone be concerned, chiefly depart from the 

 precedent laid down by Huxley in their less rigid adherence 

 to the single type organism chosen for study. Wherever parts 

 of this are, by adaptive change, so modified as to be non- 



' "Studies in Biology for New Zealand .Students." No. 4. "The 

 Skeleton of the New Zealand Crayfishes (Palinurus and Paranvphrops)." 

 By T. J. Parker, B.Sc, F.R.S , of the University of Otago. (Wellington : 

 Colonial Museum and Geological .Survey Department. London : 'IVubner 

 and Co.) 



typical in structure, Parker has introduced supplementary de- 

 scriptions of corresponding parts of less modified allies. The 

 necessity for this mode of procedure is now generally recognized ; 

 and the only danger to be averted in the future is that of un- 

 conscious reversion to the old condition of the '^omnium 

 gathenim of scraps." Let the type organism be always adhered 

 to as closely as possible. Prof. Parker has exercised, in the 

 matter, a wise discretion ; and, having availed himself of the 

 researches of Boas, has given to the world of carcinologists a 

 laboratory guide which cannot fail to be of great service to 

 them. The arthropods of the genus Palinurus happen to 

 have furnished him, a few years ago, with material for original 

 observation ; the results of his inquiry are brought to bear upon 

 the needs of the beginner in the pamphlet before us, and the 

 value of the latter is thereby enhanced. 



In dealing with the morphology of the eye-stalk (and of 

 the pre-oral region generally). Prof. Parker states the alter- 

 native views, and gives the names of their leading upholders. 

 Although he adopts the belief that the ophthalmic and 

 antennulary regions of the arthropod body do not form the 

 first and second metameres, and introduces, in accordance there- 

 with, a revised nomenclature, his remarks, when dealing with 

 the real point at issue, are so framed as to leave the mind of the 

 student unbiassed. And moreover, he has so arranged his book 

 that consideration of this vexed question in morphology is 

 deferred until the concluding paragraph. This is as it should 

 be. He naively summarizes the position in the words : — 



"The fact of the eye-stalk bearing a flagellum seems to prove 

 conclusively that it and the antennule are homologous. The 

 question then resolves itself into this : Are the eye-stalks and 

 antennules appendages in the ordinary sense, i.e. lateral offshoots 

 of the first two metameres, or are they to be looked upon 

 as prostomial appendages comparable with the tentacles of 

 Chastopods and the antennie of insects ? " 



Mindful of comments upon the general question raised in 

 the above, which have already appeared in this journal (Nature, 

 vol. XXXV. p. 506), we are of opinion that equally good argu- 

 ments are still to be adduced on both sides. The extraordinary 

 facts of development of the invertebrate nervous system which 

 are now accumulating, render it doubtful if we are justified in 

 regarding the prostomium as something so very different from 

 the rest of the body as we are wont ; and we are led to ask 

 whether it may not merely represent a precociously differentiated 

 portion of the common perisoma ? If there is any truth in the 

 belief that the symmetry of the bilateralia is a laterally com- 

 pressed radial one, the probability that the prostomium may 

 represent that which we suggest becomes vastly increased ; and 

 it is worthy of remark that that lobe in some Chietopods 

 {Nemodrihis, Phreoiyctes) so far conforms to the characters of a 

 body segment as to become externally subdivided. Nor must it 

 be forgotten that the Catovietopa bear (especially the Ocy podidcr), 

 an optic style which would appear to present us, in its variations, 

 with a series of conditions transitional between that of the eye- 

 stalk of Milne-Edwards's Palinurus (to which Parker appeals 

 in seeking to show that that appendage and the antennules are 

 homologous) and that of the ordinary podophthalmatous forms. 

 We congratulate the students of the University of Otago upon 

 the good use which, in their interests, their Professor has made 

 of the advice of his distinguished master. We cannot, however, 

 allow to pass unnoticed the statement (p. 7) that the seventh 

 abdominal somite (by which term Prof. Parker designates the 

 telson) bears appendages only in Scyllarus. This is not the 

 case, as has been previously pointed out in these pages (Nature,. 

 vol. xxxii. p. 570). The supposed appendages, did they exist, 

 would be at least peri-proctous in position ; and, as there is reasoa 

 to believe the antennules (which Parker, be it remembered, admits 

 to be serially homologous with the ophthalmites) to have been 

 originally peri-stomial, if not meta-stomial, the supposed peri- 

 proctous appendages might, with equal reason, be denied 

 homology with the other abdominal members. 



Finally : the altered position of the sterna in the anterior 

 cephalic region and the consequent displacement of their ap- 

 pendages is said to be "a result of the cephalic flexure^ by 

 which, in the embryo, the anterior cephalic sterna become bent 

 strongly upwards." Allowance has not yet been made, in dealing 

 with this question, for the fact that, in the Decapods, these 

 changes are greatly exaggerated by the general enlargement of 

 the cephalo-thoracic region, consequent upon the aggregation 

 therein of the more important and specialized viscera, and upoa 

 specialization of the thoracic appendages for ambulation. 

 1 G. B. H. 



NO. 1082, VOL. 42J 



