DYNAMICS OF MORPHOGENESIS 163 



Stage II and the time when disintegration of the marginal regions 

 of the body is completed. In Stage III the disintegration has 

 spread from where it first attacked the animal or piece and new 

 areas of disintegration may have appeared; the lateral margins 

 begin to disintegrate but the original form is still maintained. 

 Parts of the body may still show motor activity at this stage. 



Stage IV. The characteristic feature of this stage is the com- 

 plete disintegration of the marginal regions and the loss of the 

 original form which follows. The whole animal or the longer 

 piece usually becomes more or less cylindrical, the shorter piece 

 a rounded mass. During this stage the epithelium and pigment 

 disappear, the dorsal surface preceding. This stage passes into 

 the following. 



Singe V . This is the last stage on which observations are made. 

 It is reached when the epithelium and pigment are complete!}^ 

 gone and when all parts have undergone the swelling and change 

 in appearance. This stage I believe marks the completion of 

 the process of dying which began in Stage II. It is followed 

 within a short time, ranging from a few minutes to several hours, 

 according to temperature, age of w^orm, etc., by separation of the 

 tissues, disintegration of cells and gradual disappearance of the 

 mass until all that remains are microscopic particles suspended 

 in the fluid or on the bottom. 



In whole worms, where certain regions of the body die much 

 earlier than others, the different regions pass through the various 

 stages at different times. The head, for example, may undergo 

 complete disintegration before the middle regions of the body, 

 i.e., the posterior regions of the first zooid, are dead. In record- 

 ing such cases Stage II represents the first appearance of disin- 

 tegration in any region, Stage III the beginning of marginal dis- 

 integration behind the head or in the posterior zooids, and Stage 

 IV the completion of the marginal disintegration and the change 

 in shape. Here then Stage III may be disproportionately long 

 since different regions of the body possess different resistance. 

 It makes little difference, however, just what each stage includes, 

 provided it includes the same things in all cases. All that is 

 desired is to determine as accurately as possible the time of death. 



