486 



Pharynx. In some forms some or all of the pharyngeal folds fail 

 to develop, e. g. in Dendrodoa and Pelonaia. 



Gonads. The features that have been used are (1) size, (2) num- 

 ber, (3) whether found on one or on both sides of the body, and (4) 

 whether mono-sexual or bi-sexual. 



Sluiter has well shown that size and number are practically use- 

 less. As there is every possible gradation in size, this feature is not 

 readily applicable. The number of gonads is of some value. There is 

 great constancy in those species possessing only one gonad on each 

 side. AVhere two on each side is the rule, there is little variation. The 



Paratona elata 



Cnemidocarpa joannae 



Pandocia fibrosa 



Fig. II. Diagrammatic transverse sections of gonads, vd, vas deferens; ve, vas 

 efferens; ov, ovary; od, oviduct; te, testis. 



eases in which only one or three occur on a side are rare. They are of 

 sufficient rarity to be considered abnormal. Curiously enough they may 

 be the first specimens examined. The first individual of Styela monte- 

 reyensis that I examined had only one gonad on the left side and three 

 on the right ; the first of Katatropa uclueletensis had only one on the 

 right side and two on the left, of which one was imperfectly developed. 

 With more than two gonads on each side there is greater variation. In 

 5 specimens of Cnemidocarpa joannae there were from 5 to 12 gonads 

 on the left side and from 7 to 12 on the right. 



Characters (3) and (4) above are undoubtedly of great value. 



Another important feature that has not been emphasized suffi- 

 ciently is the relation of the testes to the ovary in the gonad. 



The typical gonad of the Styelidae consists of a central somewhat 



