27 



freely into the interlamellar spaces ; whence it enters the vessels coursing along the 

 border of each plate, from the inner side towards the outer side (fig. 2, a) where the 

 vessel is largest. Here appears to begin the returning system of branchial veins on the 

 fore part of the base of attachment. These veins ascend and converge on each side of 

 the intestine, and traverse the pericardial sinus to enter directly the heart by the five 

 pairs of ostia at the widest posterior part of that organ. 



The muscles which divaricate the branchigerous limbs, and at the same time separate 

 the gill-plates and expand their cavities to the extent permitted by the interposed 

 columns, act as inspiratory ones, inviting the flow of blood from the abdominal sinuses 

 into the cavities of the gill-plates. This action may be supposed to take place when the 

 King-crab is moving or resting in its atmosj)here of sea-water. The muscles which 

 approximate the branchigerous plates and press them against each other and the thorac- 

 etron, will close the ciliate sHts leading to the gills, will compress those organs, and 

 tend to squeeze the blood from the reticulate interspace of their constituent lamellae. 

 Such movement must be ' expiratory,' and also effective in defending the delicate 

 surfaces of the branchial membranes from the atmosphere of muddy or sandy sea-water 

 Avhen the King-crab is burrowing either for food or concealment. 



§ 8. Reproduction of Parts. — Of the power of reproduction of limbs or other append- 

 ages, after mutilation, I have not found recorded evidence ; but such may be inferred to 

 be possessed by Liiymlus from the reproduction of the entire crust, as in other and higher 

 members of the class. According to Dr. Lockwood *, the King-crab moults several times 

 during the first year, perhaps five or six times between its exclusion in June to the 

 setting-in of cold weather. Like other Crustacea, it moults more frequently during the 

 earlier and more rapid period of growth than afterwards. The young Limuli acquire an 

 inch in length in the first year : it is then that, after the moult, the second pair of limbs 

 are observed to have gained the sexual form in the male. " In older i/)«?;^/, just before 

 the time of exuviating, a separation occurs between the marginal rim and the perimeter 

 of the anterior shield." " To the vmaided eye the rent is imperceptible, but opens on 

 exertions of the animal ; and at this opening it emerges from the old shell "t. A specimen 

 which liad accomplished this moult measured 9i inches in the short diameter of the 

 cephaletron, while the vacated shell was but 8 inches by the same measurement. This 

 exuviation was observed in the month of August : but Dr. Lockwood gives an instance 

 of a soft Limulus having been dredged up in the month of Eebruary, whence he thinks 

 they may moult twice a year. 



§ 9. Generatice Si/siem. — In Limulus the sexes are distinct ; the male is smaller than 

 the female ; and in both, the generative organs lack those accessory parts that relate to 

 intromission in somfe higher Crustaceans. 



The ovarium is a system of ramified tubes and cavities, occupying chiefly the dorsal 

 region of the body ; it extends along the median part of the thoracetron, and expands 

 laterally in the cephaletron. 



Parts of the ovary are single and median ; the rest consists of parial symmetrical 

 lateral ramified tubes, chiefly situated in the cephaletron. 



* ' The American Naturalist,' vol. iv. No. 5. July 1870, p. 242. t Ibid. 



E 2 



