232 REVIEWS. 
fore it has lost its gills. Siredonl d o have 
its period of reproduction arrested until it has gone on a stage farther in growth and ni lost 
its gills. In any case the same species —nay, the same individual— is capable of existing in a 
State of maturity as a creature half fish and half reptile in regard to its circulation, or in a 
perfect reptilian state in which it breathes solely by — Farther, we may su se 
" nly 
and a change in these conditions inducing the opposite e Here we have for ri first time 
actual facts on which to base a theory of developm — dun "— point " the operation of 
two causes —first, the possible Retardation or A , and secondly, the 
action of outward circumstances on the organism capable of this retardat ion or acceleration. 
We here substitute for the acon to vary of Owen’s theory, the ascertained fact of repro- 
physical conditions, and for the questi ion as d the change of one species into another, the 
change of the same species from one g ther. Farther, instead of vague specula- 
tions as to possible Sp of amed animals, we are led to careful consideration of the em- 
' the s 
sts tabulated by Mr. hene Mani nay y proceed to ate the limitations 
hich his views put to the doctrine of derivation. f this the real nature 
oe Se as a possible Pid] then derivation must follow the same ien wiicdo eta- 
orphis m n and ombr youte fers? 
peci ted y have in itself A CAPACI ee Lem 
M k 1 cates Hani 
which ever 
| ti 
ee with fe influence o of external circumstances. Yet the agar eg ud r orbit of 
y to pass 
into a really bt, b A al investi- 
ng etn inferen nce. As already hinted, it is a most important point o of se siguen that when 
ain e series of embr ryonie changes of any animal, we have thereby ascer- 
tained ‘is “possibilities in regard to accelerated development lis bc sensorial in Tepara tor 
udies of scale. Now, if M 
we knew the embryonic history of every snimdt, i rec and fossi il, i in its anatom etails, 
we should be able to construct out of this a table of — affiliation of pa pas should 
he sam e d classes in 
t ty 
mh ; hy 
which they Saad msi existed in eT time, and to predict what they might become in 
ime still to come 
am heats of acceleration we have also shown to be the law of 
grow among the Nautiloids and Ammonoids. Thus the discoidal 
vus though an ancient group, do not ae during their entire 
life, from the Silurian to the Tertiary, such extensive changes in the 
septa as the Clymeniz do in the course of a single geological epoch, the 
or i 
m d is case 
precisely parallel to that of the growth of the Siredon salamander into 
the Parallelism between the ge dete of Life in the Individual and those in the 
supe se Group of the co eng Order, Te anchiata. By A, Hyatt. Memoirs Boston Soci- 
ety of Natural History, Vol. 1, Part 2, ae 
