172 A. S. PACKARD, JR., ON THE 



stream, with an occasional disc, into the base of the inner and smaller claw ; in the larger 

 claw the current passes around a sort of septum, and returns along the outer side. 



The liver arises from two branches, emptying into the alimentary canal near the two 

 anterior pairs of cardiac valves ; the anterior branch subdividing into about six main lobes, 

 their lobides all ending at an equal distance from the margin of the cephalothorax ; the 

 posterior branch sends one simide lobe into the abdomen, situated next, and extending 

 nearly to the end of the heart ; the other lobe is distributed to the posterior part of the 

 cephalothorax. The alimentary canal terminates near the base of the spine ; anteriorly it 

 forms a bulb-like swelling. The stomach moves back and forth as the oesophagus is pro- 

 truded in and out. The lobes of the liver are slenderer and more numerous than in the 

 larva. 



After a second moult of the integument, which occurred Aug. 15 — 30, the young Limu- 

 lus is .40 of an inch in length. On the 1st of July a specimen was brought me which was 

 a little over an inch and a quarter long. I think it must have been hatched the previous 

 summer, and that it was consequently about a year old ; showing its slow rate of growth. 



We are again obliged to turn to Mr. Lockwood's valuable article for information relative 

 to the number of moults Limulus undergoes. He says "the exuviation of the King Crab 

 is performed several times during the first year, and at very short intervals. How many I 

 do not know, as that must vary according to the time of hatching. But I think the young 

 produced in the latter part of June will accomplish five or six moults before the cold 

 weather comes." He thinks an individual an inch long is a year old; this is my own 

 conjecture. He also states that in February, during unusually warm weather, an adult 

 female was taken in Raritan Bay, N. J., which had recently cast its skin, as "its shell was 

 still quite soft." 



Regarding the time of sexual maturity, and the period when the external sexual charac- 

 ters appear, we must depend for our information on the researches of Mr. Lock wood. He 

 thinks that the time of puberty cannot come before the third or fourth year, and considers 

 that the latter figure may prove the minimum. It is not until this period is reached that 

 " the male undergoes its last metamorphosis." It then moults, and the anterior claws 

 assume the peculiar shape of that sex. 



Comparison with the development of other Branchiopoda. In comparing the embryol- 

 ogy of Limulus with that of other Branchiopoda, we are met by an exceptional mode of 

 formation of the germ ; just as among the Decapoda, the development of Astacus, and 

 three or four other species of crabs, and among the Amphipoda the development of the 

 fresh water Gmnmarus fluviatilis and p)ulex of Europe, is an exception to the general law 

 of development in those groups. So that it is difficult to make a comparison of the mode 

 of formation of the germ of Limulus with that of Daphnia, and other Cladocera, and the 

 Phyllopod genera, Apus and Branchipus. We have extended investigations by Zaddach,^ 

 Leydig,^ Lubbock,^ P. F. Muller* and Anton Dohrn,^ on the embryology of Daphnia, to 



1 Untersuchungen iiber die Entwicklung und den Bau der ' Philosophical Transactions, London, 1857. 

 Gliederthiere. 1 Heft. Die Entwicklung des Phryganiden- * Danmarks Cladocera, in Naturhistorisk Tidsskrift, Kjo- 

 Eies, 1854, p. 96, where he describes the development of the benhavn, 1868. 



limbs in Daphnia sima, not describing the earliest changes in ^ Untersucbiingon iiber Bau und Entwicklung dcr Arthro- 



the ego-. poden, Siebold und Kolliker's Zeitschrift fur naturwissen- 



2 Naturgeschichte der Daphniden, 18G0. schaftliche Zoologie, 1870. 



