ON PTYCHODERA FLAVA. 181 



which has been lost by all other recent Holothurids.^ But it 

 seems clear enough that the occurrence of diffuse gonads, and 

 the free, open pharynx in the sub-genus Chlamydothorax, and 

 particularly in P. flava, are facts which point conclusively to 

 the archaic character of Ptychodera. 



Summary of Principal Results. 



1 . This is the first time that an Enteropueust with a free 

 pharynx has been studied in the living condition. 



2. The Ptychodera flava of Eschscholtz (char, emend, 

 mihi) is rightly assigned by Spengel to his amended genus 

 Ptychodera, as shown by the presence of the genital pleura, 

 of external liver saccules, and by the length of the collar 

 region. 



3. P. flava belongs to SpengeFs sub-genus Chlamydo- 

 thorax, as shown by the ventral origin of the genital pleura, 

 the diffuse gonads, and the free pharynx. 



4. In the fact of the gill- slits being open directly to the 

 exterior throughout their entire length, P. flava is more 

 closely related to P. bah amen sis than to any other described 

 species. This is also indicated by the simple rows of paired 

 liver saccules as opposed to the irregular multiple arrangement 

 met with in P. erythrsea. 



5. The genus Ptychodera (referring more especially to the 

 sub-genus Chlamydothorax) probably represents an archaic 

 type, as shown by the diffuse arrangement of the gonads, the 

 free pharynx, and its littoral habitat ; and it is probably not, 

 as Spengel supposes it to be, phylogenetically younger than 

 the other genera of Enteropneusta. 



6. The gill-slits, branchial skeleton, and the temporary atrium 

 formed by the apposition of the genital pleura in Ptychodera, 

 offer a general homology to the corresponding structures in 

 Amphioxus and the Ascidians, while presenting many differ- 

 ences in the details of their structure and relations. 



7. Some of these differences are comparatively unimportant, 



1 Cf. Hjalmar Theel, "Report on the Holothuroidea," part ii, 'Chall. 

 Rep. Zool.,' vol. xiv, 1886. 



