May 19, 1881] 



NATURE 



71 



ture was found to be similar to that of excessive permanent 

 extension of iron. 



Several experiments were made to test the effect of permanent 

 torsion and permanent extension on the modulus of rigidity. 



From these experiments it was concluded :— 



1. That the loss of rigidity produced by twisting or stretching 

 a wire beyond the limits of elasticity is partly diminished by 

 rest. 



2. That the loss is more sensible with large arcs of vibration 

 than with small ones. 



3. That the influence of rest is more apparent in the case of 

 large vibrations than in that of small ones. 



4. That continual vibrating through large arcs has a similar 

 effect on the rigidity to that produced on the longitudinal 

 elasticity by heavily loading and unloading. And — 



5. That in the case of hard steel Ihe effect of vibrating through 

 a large arc for several minutes makes temporarily the rigidity as 

 determined from such vibrations greater than that determined 

 from smaller vibrations. 



The influence of an electric current and of magnetism on the 

 torsional rigidity of metals was also investigated, and the 

 following results arrived at : — 



1. The tor.-ional rigidity of copper and iron is temporarily 

 decreased by the passage of a powerful electric current, but is 

 very little, if at all appreciably, altered by currents of moderate 

 intensity. 



2. The torsional rigidity of iron is temporarily diminished to a 

 small but perceptible extent by a high magnetising force. 



3. The effects mentioned in i and 2 are independent of any 

 changes produced by the current in the temperature of the wire. 



Finally, certain critical ] oints are alluded to, there being at 

 least two such for each metal, at which sudden changes take 

 place in the ratio of the permanent extension produced by any 

 load and the load itself. 



May s. — " On the Structure and Development of the Skull 

 in Sturgeons (AciJ>eiiser rutlicnus and A. sliirio)," by W. K. 

 Parker, F.R.S. 



I must refer the reader to Prof. Salensky's ' invaluable work 

 on the development of the sterlet (Kasan, 1878), unfortunately 

 IJublished in Russian, and to the second volume of Mr. Balfour's 

 new work, for an account of the earliest stages of the Acipenserine 

 embryo. 



Even in larva: one-third of an inch in length, the cartilage 

 was becoming consolidated, and I was able to work out, by 

 sections and dissections, the structure of the cranium and visceral 

 arches ; the one specimen which was seven-twelfths of an inch 

 in length, and which was made into a large number of extremely 

 thin sections, left nothing to be desired. 



The development of the skull of the sturgeon is very similar 

 to what we find in the sharks and skates ('■ Selachians"), but 

 the suspension of both the mandibular and the hyoid arches by 

 one pier, derived from the hyoid (the hyostylic skull), which is 

 seen in the Selachians on one hand and in the Holostean Ganoids 

 and Teleosteans on the other, attains its fullest development in 

 the " Acipenseridse," or Chondrosteous Ganoids; for in them 

 the "symplectic" is a separate cartilage, and not a mere osseous 

 centre as in Lc-pidostetis and the Teleostei. 



Here I find a very noticeable fact, namely, that whilst in the 

 salmon the metamorphosis of the simple primary arches of the 

 face can be followed step by step, in the sturgeon the peculiar 

 modification of the arches show s itself during chondrificalion ; 

 the hyoid arch, from the first, is inordinately large. 



Notwithstanding the huge size of the sub-divided hyoid pier, 

 its head only articulates in the larva with the auditory capsule ; 

 later on the basal cartilage reaches it, as in the Selachians. 



But the arches that retain their normal size lend no colour to 

 the theory that the visceral arches are related by their dorsal 

 ends to the paired cartilages that invest the notochord, a state of 

 things like that seen in the ribs and in the superficial cartilaginous 

 hoops that surround the huge pharynx of the lamprey. 



Mr. Balfour has demonstratively show n that in the branch'al 

 region, when the pleuro-peritoneal cavity has been sub-divided 

 by the hypoblastic outgrowths of the pharynx, the aortic arches 

 lie inside the small temporary "head cavities," or remnants of 

 the once continuous sub-division of the body wall into an inner 

 layer, the " splanchno-pleure," and an outer layer, the " somato- 

 pleure." 



But the aortic arches mount up, on each side, outside the 



* My smallest specimens we 

 he late Mr. William Lloyd. 



: the gift of Frof . VV. Salensky, the larger of 



proper branchial arches, w hich become grooved to receive them ; 

 these arches must therefore be considered as developments of the 

 temporarily separate "splanchno-pleure"; they cannot be classed 

 with the costal arches, which are developed in the permanently 

 distinct "somato-pleure." 



My dissections and sections, both of this type and of the 

 Selachians, show, without leaving room for doubt, that all the 

 viscera', or, properly speaking, hranchial arches, mandibular, 

 hyoid, and posthyoid (branchial proper) are developed in the 

 outer walls of the large respiratory pharynx, quite independently 

 of the base of the skull and the fore part of the spinal column. 



I have at last ceased to contend for true branchial or visceral 

 arches in front of the mouth, and also to look upon the mouth 

 and the openings around or in front of it as more than mere 

 involutions of the epiblast ; the first cleft is that between the 

 mandible and the hyoid arch, the first arch is the mandibular. 



With regard to the skull, it is now very evident that the " tra- 

 beculas cranii," even in their furthest growth firwards from the 

 end of the cephalic notochord, are merely foregrmvtlis from the 

 moieties of the investing mass (the parachordals), the true axis of 

 the cranial skeleton ending under the fold of the mid-brain. The 

 "cornua trabecule," and the " intertrabecular" part or tract, 

 ave fresh shoots, so to speak of cartilage that are specially deve- 

 loped to finish the cranial box and the internasal framework. I 

 fear that my long-cherished pre-oral visceral arches will row 

 have to go down and take their place among these secondary or 

 adaptive growths. 



I may remark, in concluding this very imperfect "abstract," 

 that the sturgeon is a very important type for the moiphologist 

 to get clear light upon. 



In the Selachians the huge pterygoid foregrow th of the mandi- 

 bular arch aborts the apex of its ]>ier, \\\\oie function is supplied 

 by the hyo-mandibular ; fragments only are developed in its 

 upper part. 



In the sharks from one to three mere "rays" are developed 

 in front of the small upper remnant of the first cleft ("spiracle") ; 

 in skates there is, as a rule, a small separate piece, the true apex 

 of the arch, its "pedicle." In one kind, however, the torpedo, 

 four such fragments appear on each side, as shown by Gegen- 

 baur. In the sturgeon there is a most remarkable 1 late in the 

 common metaptei7goid region, its form is rhomboidal ; it is 

 composed of a number of well-compacted pieces of cartilage, a 

 middle series of nzygous plates, and a somewhat irregular 

 arrangement of plates right and left of these. This remarkable 

 structure only exists in the Acipenseroids ; it is not found in 

 Polyodon. 



In the Selachians the "placoid" plates or spines are not 

 brought under the influence of the chondrocranium, which has 

 neither parosteal plates applied as splints to it nor ectosteal 

 plates grafted upon it. 



In Acipeuser there are both parostoses applied to the oral 

 apparatus, and ectosteal centres in the post-mandibulnr arches ; 

 morever, along the side of the skull, in old individuals, plates of 

 bone appear as splints or parostoses, that are manifestly the 

 forerunners of the deeper plates that in the higher Ganoids and 

 the Teleostei form the proper ectosteal bony centres of the more 

 or less ossified cranial box. 



The Ganoid scutes of the sturgeon are so far dominated by 

 the huge chondocranium, that by courtesy they may be called 

 frontal, parietal, opercular, and the like ; of course such scutes 

 are not the accur.ite homologues of the bones so named in the 

 Teleostei, which at the most can only correspond to the inner 

 layer of the scute of such a fish as the sturgeon. 



The sturgeons as a group cannot be said to lie directly between 

 any one family of the Selachians and any one family ot the Bony 

 Ganoids, yet on the whole that is their position ; the Bony 

 Ganoids on the whole approach the Teleostei, especially such 

 forms as Lepidosteus and Amiei, which have lost their "spiracle," 

 and in other things are less than typical, as Ganoids. 



Larval sturgeons are, in appearance, miniature sharks : for a 

 few weeks they have a similar mouth, and their lips and throat 

 are beset with true teeth that are moulted before calcification 

 has fairly set in. Their first gills are very long and exposed, 

 but not nearly so long, or for such a time uncovered, as in the 

 embryos of sharks and skates. 



Mathematical Society, May 12. — S. Roberts, F.R.S., pre- 

 sident, in the chair.— Prof. C. Niven, F.R.S. , was admitted 

 into the Society, and the following were elected members : — I . 

 Rosenthal, B.A. Dublin, C. A. van Velzer, F. Franklin, Ph.D , 

 and Miss Christine Ladd, thdlast three of the Johns Hopkii s 



