THE HORSE FOOT CRAB. 265 
been set for a number of days, and the water was in a fine 
state of oxygenation. One difficulty I had to submit to, of 
a serious character. I could only subject the water to the 
reflected light of the sun. The direct light would in the 
summer season prove too warm, and spoil my water. The 
result, as will appear, was that the hatching was accom- 
plished very slowly, a fact which with another should be 
borne in mind while reading the following, namely, the ab- 
sence of those conditions of agitation, variation of water 
depth, and sometimes complete exposure to air and sunlight, 
consequent on the tidal flow. 
. May 26, 1869.—To-day my Limulus eggs were set for 
hatching. Yesterday was full moon. The eggs were of a 
greenish white, dull, and rather dirty looking. . My notes 
record no measurement, which I now regret. As incubation 
progressed the external shell became rapidly darker, and 
more coriaceous. But for this last fact I had becóme afraid 
that they were in process of decay. Several ineffectual ef- 
forts were made to get at the internal changes, but owing to 
imperfect instruments I gave up in despair, and determined 
to watch and wait for more advanced developments. There 
is considerable vitality in the King Crab's eggs. It will bear 
a good deal of retardation, and yet come out at last. It 
will be understood that necessarily my arrangements had a 
good deal of retarding effect. At the real amount I was 
quite surprised. Those on the surface progressed most 
rapidly. 
July 18th.—Thirty-four days after spawning. The opaque 
chorion has cracked (Pl. 3, Fig. 1) disclosing the white pel- 
lucid spherieal membrane within. Now a sight met me 
which gladdened my eyes. It was a living trilobite form. 
But of course very diminutive. Yet it could be seen with 
the unaided eye, and quite satisfactorily with a common lens. 
It is shown greatly magnified (Pl. 3, Fig. 2) in outline. 
Here the elongate character of the abdominal posterior is 
noticeable; also the excessive relative width of the thorax. 
AMER. NATURALIST, VOL. IV. 34 
