596 ON INCREASE IN COMPLEXITY [pt. iii 



much the same way as the other two in the later stages, always 

 having two regions of high susceptibility, the anterior preceding 

 before the closure of the germ ring and the posterior preceding 

 afterwards. Minor variations in susceptibility of eyes, fore brain, 

 etc., were noted. The somites in all three teleosts disintegrate from 

 each end, but more from the anterior than from the posterior. Special 

 observations were made on the heart gradients, which agreed in 

 many particulars with subsequent work by the same author on the 

 gradients of the embryonic heart of the chick, e.g. the venous end 

 was the more susceptible, and the gradient decreased towards the 

 arterial end. 



Hyman was able to draw several conclusions from this work 

 important for pure embryology, such as that, in different teleost 

 embryos, the amount of material contributed to embryo formation 

 by the germ ring is variable, being very little in the cunner and con- 

 siderable in the minnow. This reconciled the views of older workers, 

 such as Morgan; Sumner; and Kopsch. These points, however, 

 together with the fact that her results gave no support to the 

 concrescence theory, are not so important for the present purpose as 

 the delineation of the regions of high susceptibility for comparison 

 with other embryos. The double gradient (anterior and posterior 

 zones of high susceptibility) is also regarded by Child & Hyman as 

 important for a comparison which they make between segments in 

 segmental animals and separate individuals, suggesting that, whereas 

 in annelids the posterior zone is permanent and never comes under 

 the control of the anterior zone, in vertebrate embryos it eventually 

 dies away, so that further segmentation ceases. This need not, 

 however, detain us here. 



In the same paper as has already been mentioned, Hyman 

 measured the rate of oxygen consumption of Fundulus eggs during 

 their development. Unfortunately, the figures do not give us any 

 information which would either support or weigh against Child's 

 theory of metabolic gradients. Owing to the small size of the embryo, 

 the determinations had to be expressed in relation to looo eggs 

 (i.e. embryos + yolks), and, as we have no idea how the wet and 

 dry weights of the eggs or the embryos were varying during this 

 period, we cannot calculate the metabolic rate. This work will be 

 discussed in detail in the section on the respiration of the embryo. 

 Hyman also made a summary of the teratological results which had 



