282 The American Naturalist. [March, 
The Cannon-Bone of Ruminants.—The usually accepted view 
has been that the cannon-bone of the hind leg of the ruminants 
consists of the coalesced metatarsals three and four, and that the 
metatarsals two and five become lost during development. J. E. V, 
Boas now offers evidence > which goes far to show that in these forms we 
are to recognize besides the coalesced metatarsalia three and four the 
upper ends of metatarsalia two and five. His views are thus in corre- 
spondence with those arrived at by various authors in the fossil 
orms. 
EMBRYOLOGY.! 
Embryology of Limulus.—Professor J. S. Kingsley publishes 
a preliminary note on the ‘‘ Ontogeny of Limulus.’’ ? The segmentation 
nucleus undergoes several divisions before any signs of segmentation 
of the egg are seen at the surface. The resulting nuclei migrate 
towards the surface, and forty hours after impregnation the egg itself 
begins to cleave, so that the whole becomes separated into cells, with 
a nucleus in each segment, and a blastoderm forms on one side of the 
egg. Here the cells are smaller, forming a primitive cumulus, com- 
parable to that of spiders. A circular spot appears in the center 
of the cumulus, becomes triangular, elongates, and forms a shallow 
groove,—the blastopore. The mesoderm forms along its margins. 
Later six pairs of segmentally arranged sensory thickenings appear 
outside the legs. The first pair gives rise in the median ocelli, the 
second to a new sense organ, the third disappears, the fourth remains 
as the ‘dorsal organ,” the fifth gives rise to the paired compound 
eyes, the sixth is evanescent. All of these organs are connected by 4 
longitudinal nerve. The facts obtained from the ontogeny point to 4 
close relationship between Arachnids and Limulus. 
Embryology of Phalangium.—A preliminary note on the 
early stages of Phalangium is published by Victor Faussek.* The 
breaks up into a solid mass of cells, each filled with yolk, and each 
containing a nucleus. From the large superficial cells there separates 
by delamination small cells, while the resulting small cells form the 
blastoderm, which soon appears on one side of the egg. The targ! 
5 Morph. Jahrbuch., XVI., p. 526, 1890. 
} Edited by Dr. T. H. Morgan, Johns Hopkins University, Baltimore, Md. 
2 Zoologisches Anzeiger, No. 345, 1890. 
3 Zdol. Anz., January, 1891, No. 353. 
