290 REPORT—1904. 
respect not only between embryos grown in different solutions, but 
even between those grown in one and the same medium. There is a 
spacious bilateral archenteron extending in front of the dorsal lip of the 
blastopore: 
The mesoderm is formed in the usual manner, partly from cells in the 
neighbourhood of the blastoporic lip, partly by differentiation of yolk- 
cells which have been pushed into the segmentation cavity. This cavity 
is obliterated. 
The notochord is not formed in quite the normal fashion, that is, by 
the splitting off of a rod of cells from the roof of the archenteron. Its 
formation in these monsters recalls the mode of its origin in the Urodela, 
Gymnophiona, and Petromyzon ; a median strip of the whole thickness 
of the roof of the archenteron is folded off, while cells from the sides grow 
beneath this to complete the definitive roof of the gut. 
The following organs are formed, though their development is often 
abnormal ; as, for example, when the cavity of the optic vesicleis reduced 
to a narrow slit :— 
The suckers; the optic vesicles, but not the lens; the auditory 
vesicle ; the infundibulum ; the pituitary body; the neural crest, with 
the vagus and trigeminus ganglia; the protovertebree ; a trace of the 
splanchnoceel ; the liver diverticulum. 
Normal histological differentiation may set in, for example, in the 
cells of the suckers and of the notochord. 
The notochord seems to retain its capacity of growth in the direction 
of its long axis ; it becomes bent and twisted in both a vertical and a 
horizontal plane. 
Ultimately degeneration and disintegration of the embryonic tissues 
sets in. The parts most commonly affected first are the medullary 
groove (or tube), the lips of the blastopore (when this has not closed), 
and the general ectoderm. Later the yolk-cells become altered and die. 
These changes are as follows :— 
(1) Grey degeneration, seen usually in the medullary groove. The 
cells protrude above the surface ; the pigment retreats to the inner end, 
leaving the cells white ; the cells fall out. 
(2) Wrinkling and pitting of the surface. The ectoderm is thrown 
into folds ; the cells are cast out. 
(3) Liquefaction of the yolk-cells by fusion of yolk-granules. 
This cellular disintegration is accompanied by degeneration of the 
nuclei. 
It is a common occurrence for these dying embryos to become con- 
stricted into two parts, one portion being pushed bodily through the 
vitelline membrane into the jelly as an ex-ovate. 
III. The embryo is able to elongate, but development is abnormal, 
particularly in the closure of the blastopore and medullary folds. 
Degeneration and death eventually follow. 
(a) Sodium chloride and sodium nitrate. 
There is a large persistent yolk-plug. 
The medullary folds fail to close, most frequently in the region of the 
brain. The floor of the medullary groove here undergoes the process of 
