490 PROF. OWEN ON THE ANATOMY 
etron. The indications of segmental structure on its dorsal surface, or carapace, are mar- 
ginal and transversely linear, due chiefly to the hepatic lobes seen through the transparent 
skin; they denote six segments (cut, fig. 5). The buds of the anterior pairs of thoracetral 
limbs (ib. viri) next appear; and the joints of the longer cephaletral ones (rr-vii) 
become more marked. The embryo now rotates in its moulted protoderm. The 
definition of the thoracetron is speedily followed by the out-budding of a third pair of 
limbs. The compound eyes (cut, fig. 7, 1) appear as white dots; the ocelli (ib. a) are 
next discernible on the first segment. Behind the six cephaletral segments there are 
now eight thoracetral ones, and a ninth, pleonic, as broad as long. These are defined 
upon the periphery of the spherical embryonal mass. 
At this stage the chorion cracks; and sea-water endosmotically filtering through the 
protoderm, expands it, and allows free flotation to the rotating embryo. The heart 
appears as a pale streak, extending from the front edge of the cephaletron to near the 
opposite end of the thoracetron, along the median dorsal depression. The reaction of 
the sea-water upon the intraovular embryo, combined with excentrie pressure through 
growth, is manifested by the peeling off of a thin skin. The body becomes flattened as 
it broadens; the median region of the tergum rises, and interrupts the segmental lines ; 
the compound eyes project from the boundary ridges between the median and lateral 
regions, and the three-lobed character of the carapace is manifested. The ‘sternal’ 
surface recedes from view, in profile, and the hollow (cut, fig. 8, A) lodging the mouth 
and maxillipeds begins to be established. At this stage the spatulate appendages of 
the penultimate joint of the limb vit. appear as simple spines, and the terminal forceps 
is complete in this, as in the antecedent limbs. Now, also, the ‘chilaria’ appear as 
rather flat oval tubercles closing behind the sternal or “oral” groove (fig. 8, y). 
In this state of development the young Limulus escapes from the * protoderm’ (amnion, 
endochorion) The cephaletron is about half as long as wide, its margins are fringed 
with cilia, from pits on their upperside. About three weeks after hatching, the skin is 
shed; the thoracetron shows its marginal notches and movable spines, the latter shorter 
than in the adult. A fourth pair of lamellate limbs appears. The pleon now projects 
from the mid notch of the eighth segment, its base embracing the vent, which opens 
upon it; its apex is subacute, and its length about thrice its basal breadth. A second 
moult was observed between the middle and latter end of August. 
The sum of these observations shows the progressive acquisition of the mature cha- 
racters of the King-crab without undue development attended with subsequent loss or 
curtailment of parts in relation to a phase with habits of life markedly different from 
those of the adult—in other words, without ‘ metamorphosis.’ In this respect Limulus 
follows the course shown in Astacus fluviatilis + and some other Crustacea, as well as in 
Arachnids and Cephalopods. | 
Dr. Anton Dohrn } has also recorded notes on the ovum, embryo, and young of 
+ Comp. fig. 4 with fig. 136, p. 336, * Lectures on Invertebrata, and fig. 5 with fig. 137, p. 337, ib. 
i “Untersuchungen über Bau und Entwickelung der Arthropoden," ‘Jenaische Zeitschrift, Band vi. Heft 4 
(1871), p.582. Of other contributions by this excellent observer to the embryology of the Crustacea I may cite:— 
‘Die embryonale Entwicklung des Asellus aquaticus? 8vo, 1867; * Untersuchng. üb. Anat. u. Entwicklg. d. Arthro- 
