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



sternal groove. In adult life, they are moveable at their bases and armed on their inner 

 side with powerful spines, like those on the maxillipeds ; hence they serve two purposes, 

 namely, of completing the circumoral cavity, in which the food is retained by the spines 

 of the surrounding walls, and of directly aiding in triturating the food and preparing 

 it for deglutition. Savigny has considered it as functionally a sort of inferior lip. It 

 apparently corresponds to the postoral plate or epistoma of Hall (metastoma of Huxley), 

 of the Eurypteridse, where it forms a solid, heai't-shaped, oval plate ; its position seems 

 nearly identical, though set farther fi-om and partially covering the base of the last pair of 

 feet. Its great development and unpaired form seem correlated to the diiference in the 

 form and functions of these feet as compared with those of Limulus. Woodward says of 

 the metastoma that "it no doubt represents the labium, and serves more effectually to en- 

 close the posterior part of the buccal orifice, being found exterior to the outside edges of the 

 ectognaths or maxillipedes." Latreille has applied the term epistoma to the clypeus of 

 insects, and as this postoral plate is in no way homologous to the labium or second maxillae 

 of insects, the term metastoma applied by Huxley is very appropriate. 



The ocelli are situated in an earlier period of this stage than that represented by fig. 24, on 

 the under side of the head just in advance of tlie mandibles, and are at this time white and 

 irregular in shape, being a little longer than broad. A little later they appear on each 

 angle of the front edge of the cephalothorax ; the edge being afterwards expanded and ex- 

 tended, so that as in fig. 24 they are placed a little way in from the edge. The eyes also 

 are at first rounded white tubercles, becoming in more advanced specimens black along 

 the front edge. The protoderm measures at this period, .13 of an inch in diameter. Of 

 the eggs laid in the middle of May one was hatched June 30th, the majority came out of the 

 egg about the 14th of July, and the remainder kept hatching until the last of September, 

 in my jars. In the succeeding summer (July, 1871) the hatching jar, in which the water 

 had remained unchanged since the previous October, and with no weeds to oxygenate the 

 water, contained several embryos in eggs laid during the preceding year, in different though 

 advanced stages of development, and also several larvae hatched during 1870, though in a 

 torpid state, due probably to the little air in the water. I much doubt whether the 

 eggs of any other living crustacean would show as much vitality. It should also be 

 noticed that these eggs had not probably grown during the winter, but remained as 

 it were in a state of suspended animation from October to July, a period of nine 

 months. These facts confirm the remarkable observations of Rev. Dr. Lockwood on 

 tlie wonderful vitality of the eggs of Limulus. He remarks, " at the close of the warm 

 season last year [1869], my jars must have contained not less than two hundred young 

 Limuli. We have already said that so soon as hatched, the young burrow like the adult ; 

 hence the rareness of an opportunity to witness the casting of the skin. Hoping to con- 

 tinue ray observations upon the growth of my interesting family the ensuing year, the jars 

 were carefully put away. Little regard, however, was paid to temperature, which, on 

 several occasions, went down to the freezing point. On the 3d of May, 1870, I emptied 

 the jars to see how my charge was getting on, when lo, not one of the last years' hatching 

 was alive ! but wonderful to say, at least a dozen little fellows, all hatched this spring, and 

 all alive, had taken their place. With these were also at least thirty eggs, in different, 

 but all in advanced stages of incubation. In some of them, the young could be plainly 

 seen revolving. The fact is, these eggs had been at the bottom of the hatching jar, and 



