494 PROF. OWEN ON THE ANATOMY 
more of the lamelliform limbs, on the second and third of which the gill-plates have 
‘begun to appear*. This is far from being a ‘Trilobite;’ and nothing is gained to 
science by putting figurative expressions for facts. In the inductive school of biology, 
the notion that a higher form traversed a series of lower forms in the course of its 
development has ceased to be set forth, save under duly modified terms+. I am 
under the impression (and it is an agreeable one to the mind searching solely for intel- 
ligible and demonstrable conclusions) that few now dispute the fact that each individual 
of a given species is such ab initio, and takes its own course to the full manifestation of 
its specifie characters, agreeably with the nature originally impressed upon the germ. 
A King-crab does not, any more than a perch, a dog, or a man, begin to be such only 
when the zoologist discerns the respective characters of the parent, but is such even 
before embryologists detect their earliest dawn. The embryo Limulus derived its nature 
and the potency of growth according to the specific pattern from the moment of the 
impregnation ; and each step of development moves to that consummation as its end 
and aim i. The generic character is indeed significantly soon shown in the budding 
Limulus. 
The first steps, like those in all segmental (whether articulate or vertebrate) animals, 
recall the work of crystallization, and illustrate growth by repeated samenesses. These 
-show the results of formifaction, aggregated in series of similar heaps of organic atoms 
(fig. 4) before the specific affinities begin formally to operate thereon and plainly to 
show themselves to the eye. No sooner, however, can one of these heaps, or pairs of 
heaps, be recognized as budding limbs, than in such series the first is seen to be Limuline 
by its halting growth (fig. 6, 11); the second (111) pushes on outside these, the basal 
joints of the *antennules ' (11) being at the interspace of those of the ‘antennæ ' (fig. 8 
III), according to the King-crab's pattern. 
Further back in that interspace opens the mouth (fig. 6). It is at no developmental 
stage typical as a transient manifestation of the ordinary position of the mouth in an 
annulose animal; that is to say, it is at no time terminal—but as soon as it opens 
(fig. 4), testifies by its inferior position that it is the mouth of a Limulus, not of any older 
or any lower form. 
Thus, in the existing representative of Xiphosura, the embryo or larva is neither a 
Nauplius nor a Zoéa, nor a Trilobite: it is a Limulus, exhibiting the characters of such in 
stages of development or growth corresponding to the period of incubation at which the 
immature creature may be examined. 
$11. Conclusion.— that the Trilobite, like the Limulus, possessed articulate Hit] 
has, however, been advocated not only by interpretation of appearances in an exceptional 
instance, but by appeal to the laws of coexistence $. I would submit, however, the 
* Packard, loc. cit. p. 170, pl. v. fig. 26. 
t See the concluding Lecture of my course oh * Invertebrata,” of 1843, 8vo, p. 367. 
t Anat. of Vertebrates, vol. i. p. xxi 
$ * The large compound sessile eyes, T the hard, shelly, many-segmented body, with its compound caudal and 
head.shield, differ from any known Phyllopod, but offer many points of analogy with the modern Isopods; and one 
would be led to presuppose the Trilobites possessed of organs oflocomotion of a stronger texture than mere bran- 
chial frills."—H. Woopwarp, Geological Magazine, vol. viii. p. 523 
