33 



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. viii) next appear; and the joints of the longer cephaletral ones (ii-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, i) appear as white dots ; the ocelH (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 intra-ovular embryo, combined with excentric pressure through 

 gi'owth, 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 vii. 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, ^). 



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 Limuhts 

 follows the course shown in Astacus Jluviatilis f and some other Crustacea, as well as in 

 Arachnids and Cephalopods. 



Dr. Anton Dohrn t has also recorded notes on the ovum, embryo, and young of 



t Comp. fig. 4 with fig. 136, p. 336, ' Lectures ou Invertebrata,' and fig. 5 with fig. 137, p. 337, ib. 



X " Untersuchungen iiber Bau und Entwickehmg der Arthropoden," ' Jeuaische Zeitschrift,' Band vi. Heft 4 

 (1871), p. 582. Of other contributions by this excellent observer to the embiyology of the Crustacea I may cite ; — 

 ' Die embryonale Entwicklung des AseUiis aquaticus,' 8vo, 1867 ; ' TJntersuchng. lib. Anat. u. Eutwicklg. d. Arthro- 



