PLATE 1 
EXPLANATION OF FIGURES 
1. Sketch of specimen, flattened and mounted in balsam; dorsal view; actual 
length 1.43 millimeters, a, pharynx; h, esophagus; c, eye; d, sperm sac; e, e, em- 
bryo consisting of a central mass of cells surrounded by a yolk ; others will be found 
to which no index lines point; for example, there is one almost exactly in the mid- 
dle of the body and another j ust behind the embryo to which the index of / points. 
The latter appears to be on the point of dividing. A similar stage of development 
will be found in front of r. f, embryo with large cells at opposite poles and sep- 
arated by yolk; another will be found on the median side of the sperm vessel, 
while between the latter and the anterior end of the left ovary is one which is a 
little farther advanced, h, ovum with a large germ cell enclosed in yolk; k, col- 
lapsed embryonic capsule ; another is shown just behind n; I, twin embryos enclosed 
in the same embryonic capsule; others are shown in various parts of the body; m, 
yolk cells; n, single young in capsule; o left ovary; p, mass of cells in capsule, 
all the yolk is absorbed; q, early stage of twins enclosed in yolk; r, this represents 
a stage in development just before division into two masses of cells; z, young 
escaped from capsule and wandering about in the mesenchyme. 
2. Sketch of specimen which had been killed under slight pressure over flame 
and was lying in sea-water, a, two large cells with coarsely granular yolk; 6, 
twins, ciliated, but the eyes have not yet appeared. In the anterior capsule there 
are a few yolk granules which have not yet been absorbed. This is also the case 
in the capsule median to a. In the posterior one all the yolk has been absorbed. 
c, twins, ciliated and with eyes. There are three other pairs shown; it is to be 
noted that in each case some of the yolk has not been absorbed. 
Actual length 1.61 millimeters. 
3. Another, also in sea water; actual length 1.30 millimeters, a, brain; b, ovum 
with a germinal cell at each end separated by yolk ; c, sperm sac ; d, probabfy a part 
of the ovary distorted by pressure; e, embryo consisting of two masses of large 
cells separated by yolk and small cells. This form has originated from a condition 
like that represented in 6; it is about ready to separate into a pair of twins. /, this 
shows the division completed which is faintly indicated in e. Another represent- 
ing a similar stage is just behind/, h, a pair of twins, ciliated but eyes not yet 
developed; J, twins ciliated and with eyes. It will be noticed that all the young 
in this specimen have divided in such a way as to include the yolk, k, a granular 
body, probably an ovum in which the nucleus is concealed by the mass of yolk. 
4. Longitudinal, horizona! section a, pharynx; b, esophagus; c,c, intestine; 
e, segmenting ovum similar to/, fig. 1;/, segmenting ovum, large cells at oppo- 
site poles;/, k, I, m, ciliated embryos; o, ovary. Length 0.97 millimeter. 
5. Ventral view of head showing mouth and a preoral furrow; sketched from life. 
