GRAFTING AND REGENERATION 189 



eggs or blastulae, and obtained perfect single individuals from two 

 fused blastulae. He finds that if the fusion takes place at an early 

 stage the resulting embryo is less likely to show its double origin 

 than when older blastula stages are united. Zur Strassen has also 

 observed giant embryos of ascaris that arise by a fusion of two eggs. 

 Loeb has found that the eggs of chaetopterus, which can be made to 

 develop parthenogenetically in certain salt solutions, often stick to- 

 gether and produce giant embryos. 



