830 REPORT—1 890. 
than they were ; the international brotherhood of science is now fully established, 
and the fault will be ours if the material and opportunities now forthcoming are 
not rightly and fully utilised. 
By judicious selection of groups in which long series of specimens can be 
obtained, and in which the hard skeletal parts, which alone can be suitably pre- 
served as fossils, afford reliable indications of zoological affinity, it is possible to 
test directly this correspondence between paleontological and embryological 
histories, while in some instances a single lucky specimen will afford us, on a 
particular point, all the evidence we require. 
Great progress has already been made in this direction, and the results 
obtained are of the most encouraging description. 
By Alexander Agassiz a detailed comparison was made between the fossil 
series and the developmental stages of recent forms in the case of the Echinoids, a 
group peculiarly well adapted for such an investigation. The two records agree 
remarkably in many respects, more especially in the independent evidence they 
give as to the origin of the asymmetrical forms from more regular ancestors. The 
gradually increasing complication in some of the historic series is found to be re- 
peated very closely in the development of their existing representatives ; and with 
regard to the whole group, Agassiz concludes that,! ‘comparing the embryonic 
development with the palzontological one, we find a remarkable similarity in both, 
and in a general way there seems to be a parallelism in the appearance of the fossil 
genera and the successive stages of the development of the Echini.’ 
Neumayr has followed similar lines, and between him and other authorities on 
the group there seems to be general agreement as to the parallelism between the 
embryological and paleontological records, not merely for Echini, but for other 
groups of Echinodermata as well. 
The Tetrabranchiate Cephalopoda are an excellent group in which to study the 
problem, for though no opportunity has yet occurred for studying the embryology 
of the only surviving member of the group, the pearly nautilus, yet owing to 
the fact that growth of the shell is effected by addition of shelly matter to the 
part already present, and to the additions being made in such manner that the 
older part of the shell persists unaltered, it is possible, from examination of a single 
shell—and in the case of fossils the shells are the only part of which we have exact 
knowledge—to determine all the phases of its growth; just as in the shell of 
Orbitolites all the stages of development are manifest on inspection of an adult 
specimen. 
In such a shell as Nautilus or Ammonites the central chamber is the oldest or 
first formed one, to which the remaining chambers are added in succession, Tf, 
therefore, the development of the shell is a repetition of ancestral history, the 
central chamber should represent the palontologically oldest form, and the re- 
maining chambers in succession forms of more and more recent origin. Ammonite 
shells present, more especially in their sutures, and in the markings and sculpturing 
of their surface, characters that are easily recoenised, and readily preserved in 
fossils ; and the group, consequently, is a very suitable one for investigation from 
this standpoint. 
‘Wiirtenberger’s admirable and well-known researches* have shown that in the 
Ammonites such a correspondence between historic and embryonic development 
does really exist ; that, for example, in Aspidoceras the shape and markings of the 
shells in young specimens differ greatly from those of adults, and that the characters 
of the young shells are those of palezontologically older forms. 
Another striking illustration of the correspondence between the palzontological 
and developmental records is afforded by the antlers of deer, in which the gradually 
increasing complication of the antler in successive years agrees singularly closely 
with the progressive increase in size and complexity shown by the fossil series from 
the Miocene age to recent times. 
' A. Agassiz, Paleontological and Embryological Development, ‘ An Address before 
the American Association for the Advancement of Science.’ 1880. 
* L, Wiirtenberger, ‘Studien iiber die Stammesgeschichte der Ammoniten. 
Ein geologischer Beweis fiir die Darwin’sche Theorie.’ Leipzig, 1880. 
Ay 
