APPENDIX. 395 
basket (respiratory cavity); (/) cavity of the body; (m) muscles; 
- (n) testicle (in the ascidia united with the ovary into a herma- 
phrodite gland); (0) anus; (p) genital orifice; (q) well-developed 
embryos in the body cavity of the ascidia; (r) rays of the 
dorsal fin of the amphioxus; (s) tail-fin of the amphioxus; (w) 
roots of the ascidia. 
Plate XII. shows the Ontogenesis, or the individual development 
of the Ascidia (A) and the Amphioxus (B) in five different 
stages (1-5). Fig. lis the egg, a simple cell like the egg of 
man and all other animals (Fig. A 1 the egg of the ascidia, Fig. 
B 1 the egg of the amphioxus). The actual cell-substance, or 
the protoplasm of the egg-cell (z), the so-called yolk, is sur- 
rounded by a covering (cell-membrane, or yolk-membrane), 
and encloses a globular cell-kernel, or nucleus (y), the latter, 
again, contains a kernel-body, or nucleolus (#); when the egg 
begins to develop, the egg-cell first subdivides into two cells. 
By another sub-division there arise four cells (Fig. A2, B 2), and 
out of these, by repeated sub-division, eight cells (vol. i. p. 190, 
Fig. 4 0, D). By fluid gathering in the interior these form a 
globular bladder bounded by a layer of cells. On one spot of its 
surface the bladder is turned inwards in the form of a pocket (Fig. 
A4,B4). This depression is the beginning of the intestine, 
the cavity (d 1) of which opens externally by the provisional 
larval-mouth (d 4). The body-wall, which is at the same time 
the stomach-wall, now consists of two layers of cells—the 
germ-layers. The globular larva (Gastrula), now grows in 
length. Fig. A 5 represents the larva of the ascidia, Fig. B 5 
that of the amphioxus, as seen from the left side in a somewhat 
more advanced state of development. The orifice o2 the intestine 
(2 1) has closed. The dorsal side of the intestine (d 2) is con- 
cave, the ventral side (d 3) convex. Above the intestinal tube, 
on its dorsal side, the neural tube, the beginning of the spinal 
marrow, is being formed, its cavity still opens externally in front 
(g 2). Between the spinal marrow and the intestine has arisen 
the spinal rod, or chorda dorsalis (Notochord) (c), the axis of the 
inner skeleton. In the larva of the ascidia this rod (c) proceeds 
