488 PROF. OWEN ON THE ANATOMY 
The slightest obstacle turns it on its back, when, not having this organ (which the adult 
uses so effectively in such emergency), the little thing begins a vigorous flapping of the 
branchial plates. "This causes it to rise in the water; then, by ceasing the agitation, it 
at once descends with a chance of alighting right side up" *.  Eighty-two days after 
spawning, a young Limulus moulted. ** A few minutes sufficed for it to withdraw itself 
from its baby-suit; in this act it rested a little while, with the caudal appendage, now 
formed, only half withdrawn from the old shell” +. 
The extricated animal is + of an inch in width, and its tail is + of an inch in length. 
The tail is formed bent under the thoracetron, is at first curved, and “requires some 
hours to straighten out"1. The setaceous fringe of the thoracetron is replaced by teat- 
like or half-developed spines. The spiny fringe of the cephaletron is gone. The tail is 
at first somewhat stumpy, almost ovoidal in transverse section, * more distinctly marked 
with lines of segmentation than is that of the adult"$. As the young Limulus “ tra- 
velled on the mud before this moult, it made tiny rows of toe-tracks, leaving a plain 
unmarked space between the rows. Now it moves with tail depressed, and makes a 
median line, dividing the toe-tracks into two series ” ||. 
The year following the collecting of the ova, Dr. Lockwood records the interesting fact 
that certain ova at the bottom of one of the jars, “ which had never been in contact with 
the sunlight,” still retained the embryo alive and revolving; these having been trans- 
ferred to * new sea-water and clean sand, with a good exposure," were hatched ; and the 
larval Limulus left the egg within two weeks of a year after oviposition and impregnation 
of such egg €f. 
Dr. A. S. Packard **, from observations on impregnated ova of Limulus, transmitted to 
him by Dr. Lockwood, adds details of intraovular steps of development, and gives accept- 
able figures of these and of the excluded larva. 
Formifaction aggregates the protoplasmal beginning of the ovum into a central mass 
Fig. 1. 
Fig. 2. 
Section of i0 
(Pkd. pl. iii. fig. 9). 
* Eat 
Portion of surface 
Cell-egg of impregnated 
(Pkà. pl. iii. fig. 4), egg (Pkd. pl. iii. 
fig. 7). 
Embryo with limb-buds 
(Pkd. pl. iv, fig. 1). 
of larger and denser granules, constituting the nucleus (cut, fig. 1, b), within which is 
* Lockwood, loc. cit. p. 268. + Id. ib. + Id. ib. $ Id. loc. cit. p. 269. 
|| In quoting this observation, I am duly impressed by the “ caution for the interpreters of the * Protichnites,’ 
seeing that the same species, at different ages, may make widely different tracks.”—Lb. p. 273. 
a Id. ib. p.272. This result recalls the arrest of development of Tadpoles kept in the dark. 
* The development of Limulus polyphemus,” in Memoirs of the Boston Society of Natural History, vol. ii. 1872. 
ee excellent memoir was read November 16th, 1870.) 
