SOLENOCYTES 155 



of Amphioxus could be shown to have been inde- 

 pendently evolved, we should have to give up 

 structural resemblance as a guide to homology." 

 He says in a footnote that the only case which 

 seems to him at all comparable is that of the 

 nematocysts in Coelenterates, Planarians, and 

 Molluscs. To this case we may add the 

 myoepithelial cells in Coelenterates, Nematodes, 

 and Tunicata ; and, as Goodrich admits, the 

 flame-cells of flatworms, Rotifers, and Polyzoa 

 (Entoprocta) are probably of the same nature 

 as his solenocytes. 



I venture to interpret Goodrich's discovery 

 as a brilliant demonstration of histogenetic con- 

 vergence and submit the following explanation, 

 basing the argument on personal conviction, on 

 an appeal to known facts, and on certain general 

 considerations : 



Just as various offices are constituent parts 

 of the body politic, so various organs are con- 

 stituent parts of the animal economy. Pharynx, 

 oesophagus, crop, gizzard, stomach, liver and 

 other diverticula, intestine and rectum, are 

 constituent parts of the digestive tract of a 

 coelomate animal and are likely to appear when 

 called into requisition by the necessities of 

 adaptation and evolution ; and equally likely to 

 disappear when not specially required. I may 

 refer here to the remarkably simple digestive 

 tract of the Scombresocidse (e.g., Belone), where 



