9b THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. 
The holochroal eyes are of two kinds, one with plano-convex and one with biconvex 
lenses. The latter would seem to be mechanically the more perfect of the two, and it is 
worthy of note that the trilobites possessing the biconvex lenses have, in general, much smaller 
eyes than those with the other type. 
If, as some investigators claim, the parietal eye of Crustacea originates by the fusion of 
two lateral ocelli, trilobites show a primitive condition in lacking this eye, which may have 
originated through the migration toward the median line of ocelli like those of the Trinu- 
cleidye. 
Sex. 
That the sexes were separate in the Trilobita there can be very little doubt, but the 
study of the appendages has as yet revealed nothing in the way of sexual differences. One 
of the most important points still to be determined is the location of the genital openings. 
In many modern Crustacea, the antennae or antennules are modified as claspers, and it 
is barely possible that the curious double curvature of the antennules of Triarthrus indi- 
cates a function of this sort. The antennules of many specimens have the rather formal 
double curvature, turning inward at the outer ends, and retain this position of the frontal 
appendages, no matter what may be the condition of those on the body. Other specimens 
have the antennules variously displaced, indicating that they are quite flexible. It is conceiv- 
able that the individuals with rigid antennules are males, the others females. 
It is interesting to note that the antennules of Ptychoparia permulta Walcott (1918, pi. 
21, fig. 1) have the same recurved form. All the specimens of Neolenus, however, show very 
flexible antennse. 
Barrande and Salter laid great stress upon the "forme longue" and "forme large" 
as indicating male and female. This was based upon the supposition that the female of 
any animal would probably have a broader test than the male, a hypothesis which seems to 
be very little supported by fact. In practical application it was found that the apparent dif- 
ference was so often due to the state of preservation or the confusion of two or more 
species, that for many years little reference has been made to this supposed sex difference. 
Eggs. 
In his classic work on the trilobites of Bohemia, Barrande described three kinds of spheri- 
cal and one of capsule-shaped bodies which he considered to be the eggs of trilobites. After 
a review of the literature and a study of specimens in the collections of the Museum of 
Comparative Zoology, it can be said that none of these fossils has proved to be a trilobite 
egg, but that they may be plants. A full account of them will be published elsewhere. 
Walcott (1881) and Billings (1870) have described similar bodies within the tests of 
Calymene and Ceraurns, but without showing positive evidence as to their nature. 
Methods of Life. 
This is a subject upon which much can be inferred, but little proved. Without trying 
to cover all possibilities, it may be profitable to see what can be deduced from what is known 
of the structure of the external test, the internal anatomy, and the appendages. This can, 
to a certain extent, be controlled by what is inferred from the strata in which the specimens 
are found, the state of preservation, and the associated animals. (For other details, see 
the discussion of "Function of the Appendages" in Part I.) 
