190 
J. D. F. GILCHRIST. 
mate, sublimate-acetic, Gilson’s fluid, formalin-alcohol, alcohol, 
Fleming’s fluid, and formalin in sea-water were employed. 
Sublimate preparations seemed to be unfavourably affected, 
more especially in the yolk-laden parts; osmic acid caused 
great contraction, though the fixing was good, at least in the 
larva; the best results were obtained from 10 per cent, 
formalin in sea-water, provided care was taken to pass the 
tissue slowly through gradations of absolute alcohol and 
xylol. The passage from absolute alcohol to xylol was best 
effected by using half a dozen gradations of these up to pure 
xylol, though good results were obtained by passing the 
material from absolute, through to one-tliird and two-tliirds 
xylol to pure xylol. By the use of this method some very 
distinct preparations were procured, showing cellular struc- 
ture, of the early stages within the egg capsule, though, for 
some reason, the method was not successful in larvae hatched 
out from the egg. 
The history of the investigation into the development of 
Cep halo disc us need not be here gone into, further than 
to indicate certain points on which further information is 
desirable, or which are not beyond dispute. Masterman 
(1900) observed some segmenting eggs in the material pro- 
cured by the “ Challenger ” Expedition. Andersson (1903) 
noted the planula-like larva for the first time. Harmer (1905) 
described the eggs, heavily laden with yolk, their liolo- 
blastic and nearly equal segmentation, and suggested that 
they may give rise to solid embryos, in which the endoderm 
arises by delamination. He showed that the five body 
cavities of the adult arise at an early stage in the embryo. 
Andersson (1907) described his material more fully, and 
recorded the occurrence of a gastrula-like stage, in which 
there is a centrally placed mass of yolk with a narrow lumen ; 
he believes that this is the endoderm formed by a process of 
invagination. He also confirmed the early appearance of the 
body cavities. Scliepotieff (1909), though adding nothing- 
further towards the elucidation of the gastrula stage, con- 
firms the existence of the planula-like larva, and adds a 
