150 
KICIIAIM) ASSIIKTON. 
tube ami notocliorJ and, perhaps, gut, yet tlie delect is shown 
oil the upper part of the neural tube only. 
Ex]). V. (Operation hours after fertilisation, subsequent 
incubation for 36 J hours.) 
A similar blastoderm was injured at the edge of the horn ol' 
the junction zone 45° to the right of the middle line, with the 
result that a defect is said to have occurred in the primitive 
streak, though one cannot see much of it in his fig. 71. 
In none of the cases so far considered do the figures con- 
vince one that the spots called defects are really such, or 
have any constant relation to the spots injured. 
For instance, in the last case it is quite impossible to satisfy 
oneself that there is any injury at all from fig. 71, and text- 
fig. 17, which is a transverse section through the alle<red 
injury, shows a perfectly normal primitive streak section with 
a mass of cells or yolk, or botli, lying on the top in no way 
connected with it. This, in fact, is an “extra-ovate’^ in 
Roux’s sense that may have travelled from anywhere. My 
own experiences with such experiments have taught me how 
deceptive an extra-ovate may be. 
The results are very different to the defects figured by 
Kopsch in his Salmo embryo experiments. 
Exp. VJ. At a rather later stage — “ late gastrular stage ” 
— in which the entoderm had advanced a little further an 
injury was made at the posterior margin in the median line. 
'I'he result was a defect in the middle line at the level of 
the tenth pair of somites affecting ectoderm only. 
Exp. II was supposed to demonstrate the involution of the 
edge of the blastodisc to form the entoderm, because an 
injury to the edge made at 35| hours appeared only in the 
entoderm somewhat posterior to the nineteenth pair of 
somites. Iti Exp. VI an injury also touching tlie edge 
although made three (piartei's of an hour earlier appeared in 
the ectoderm only. How can this discrepancy be explained 
away on Patterson’s hypothesis? 
Now this one seems open to another explanation. There is 
clearly an extra-o\ate consisting of “a mass of dead cells” 
