RAC PAWT By Tele 
Development of Xipuosura (Limulus Polyphemus). Figures from A. S. Packarp, Anton Dourn, 
and ALEXANDER AGASSIZ. 
h. Dorsal vessel. ocl. Ocellus. 
i. Liver. a. Inner egg-membrane. 
m. Mouth. VIL. Seventh pair of appendages. 
mt. Metastoma. VIL. Bighth a UW 
m.  Nerve-cord. e IX. Ninth a us 
oc. Compound eye. 
1-17, 20, from Packard, Development of Limulus Polyphemus. Mem. Boston Soc. Nat. Hist., II., Pl. I1I.-V., 1872. 
1. 
2. 
3. 
wo 
10. 
il 
12. 
13. 
14. 
ib 
16 
Wie 
18. 
ng: 
Spermatozoa, magnified about 400 diameters. 
Early form of ovarian egg, magnified 130 diameters. 
Embryo within the egg. m, mouth. a, inner egg-membrane, the ‘‘ protoderm” or ‘‘ amnion” of Packard, 
“chorion” of Dohrn. Outside the inner membrane is seen the outer egg-membrane, the ‘‘chorion”’ of 
Packard, ‘‘exochorion” of Dohrn. The rudiments of the six anterior pairs of appendages have appeared. 
The anterior pair of appendages of Limulus, as shown by A. Milne-Edwards and Packard, are innervated 
from the cesophageal commissure, and are probably homologous with the mandibles of Crustacea. Balfour, 
moreover, has shown that in the spiders tle anterior pair of appendages (chelicere) in the embryo are 
innervated from a post-oral ganglion, and are equivalent to the mandibles of insects, rather than to the 
antenne as commonly supposed. Around the edge of the oval germ is a thin ridge, destined to be the 
lower edge of the carapace. 
The embryo in a later stage. Letters as before. 
. Older stage seen from below. The seventh and eighth pairs of appendages, VII, VIII, have appeared. 
Above the lower margin of the carapace are seen the indications of the somites, the sutures extending up- 
ward, but not reaching the dorsal side of the eg. The six anterior pairs of appendages have lengthened and 
become bent upon themselves. 
. Later stage of the embryo, viewed from the side. The body has now a decided ventral flexure. The ninth 
pair of appendages, IX, have made their appearance, the posterior division of the body has become 
clearly differentiated from the anterior portion, and its somites well marked. The six anterior pairs of 
appendages have become jointed. 7, liver. 
. Rudimentary gills from an older individual. 
. Terminal part of sixth pair of appendages. 
. Dorsal view of the embryo just before hatching. Trilobitic stage. The egg-membrane, ‘‘ amnion,” (the outer, 
or “chorion” of Packard, having been cast off before this period,) is not represented in the figure. The egg 
is now .13 in. in diameter. The embryo has already undergone its first moult within the egg. h, dorsal 
vessel. oc, compound eye. oc/, ocellus. Atan earlier period than that represented in this figure the 
ocelli are situate on the under side of the head, just in front of the mandibles. A little later they appear 
on the front edge of the carapace. By the expansion and extension of this edge they are finally brought 
to the upper side of the head, a little way from the front edge, as in the figure. 
Ventral view of the same stage. mt, metastoma or lower lip. 7, nerve cord. 
Terminal portion of third pair of appendages. Same stage as the two preceding figures. 
Newly hatched young, viewed from in front and above. 
The same, viewed from behind and above. 
Dorsal view of newly hatched young. The segmentation of the posterior division of the body has become 
obscured. 
Ventral view of the same. 
Seventh pair of appendages of larva, which form the operculum of the adult. 
One of the eighth pair of appendages of larva, bearing the gills. The two-jointed inner ramus is distinctly 
formed. 
Young at the time of hatching. From Dohrn, Untersuchungen uber Bau und Entwickelung der Arthro- 
poden. 12. Zur Embryologie und Morphologie des Limulus Polyphemus. Jenaische Zeitschr., VI., 
Taf. XIV. fig. 4, 1871. 
Larva, from a sketch by A. Agassiz, made at Naushon Island, Mass., Dec. 19, 1864. The line on the right 
of the figure indicates the natural length of the larva. 
. Larva after the first moult subsequent to hatching (about three weeks after hatching). It is now 4 in. 
long. The spine has acquired a considerable length. The arrows indicate the course of the circulation 
as seen in the living larva, the feathered arrows denoting the arterial currents, the simple arrows the 
course of the venous blood. The dendritic outline in the head is the liver sending two lobes backward 
into the hinder part of the body alongside the dorsal vessel, which lies in the median line. The dorsal 
vessel, is furnished with seven pairs of venous openings. Below the dorsal vessel, indicated by the fine 
lines within it, the intestine is seen extending back toward the spine. 
