448 INVERTEBEATA chap. 



embryonic rudiments into the larval organs has been most imperfectly 

 accomplished, and it is quite obvious that before much more progress 

 is made in this direction the method of whole mounts will require 

 to be supplemented by that of sections, and some means must be 

 devised for getting the embryos out of the egg-shell. 



EXPERIMENTAL EMBRYOLOGY OF NEMATODA 



Zur Strassen's descriptive paper, long as it is, pales into insig- 

 nificance beside his paper on the " T-Giants " (1906). These T-Giants 

 are abnormal embryos produced by the fusion of unfertilized eggs. 

 Tliis fusion occurs only in a very few cases in any one individual, 

 and it is the more apt to occur if the individual is subjecte'd to 

 extreme cold. The eggs first of all cohere, then at the points of 

 contact the egg-shells become softened and finally absorbed, and 

 then their protoplasmic contents are free to coalesce. In this way a 

 multinucleated mass is formed, but usually only one male cell enters 

 it and only one of the egg-nuclei is fertilized ; the others degnerate. 

 As a result, an abnormally large egg is formed, and occasionally, 

 if the shape of the egg-shell resulting from the coalescence of 

 several egg-shells is suitable, this large egg may develop into a 

 perfectly normal large embryo. 



But in many cases the composite shell is long and narrow, not 

 spherical in shape. Consequently, when the contained composite egg 

 has divided into four and taken on the form of a T (whence the 

 name T-giant), and when in the normal course of things the cell C, 

 which forms the lowest part of the beam of this T, should swing 

 upwards and come into contact with B, the narrowness of the shell 

 prevents it doing so ; and after much writhing, which bears witness 

 to the reality of the forces denominated cytotaxis, the cell C settles 

 down to continue its development in its abnormal position. 



The life of a T-giant is, however, of very limited duration. The 

 descendants of AB (the dorsal cell family) divide repeatedly, so as 

 to form an irregular vesicle of cells, the ventral cell family carry 

 out several divisions, but soon granular degeneration sets in and the 

 embryo dies. In one case, however, after the first division in the 

 ventral cell family had taken place, the whole embryo had so con- 

 tracted that it was now possible for C to swing upwards ; but this 

 swing upwards took place to the left instead of, as in the normal 

 embryo, in the median plane, and as a consequence C became wedged 

 in between a and ;S instead of between b and /8, as it should have 

 done. Nevertheless, in the further development of this embryo 

 considerable readjustment took place. Although at first the cells 

 of the ventral cell family occupied abnormal positions (mst, for 

 instance, being in front of furr), yet they glided on each other 

 till the normal position was very nearly attained, and, indeed, the 

 embryo showed every sign of developing into a normal larva until 

 it met its death by an accident. In this case it seems as if the 



