222 Charles Lincoln Edwards 



of the results obtained by Ludwig and myself, it is much to be desired 

 that Holothuria tremula be reinvestigated through the careful study 

 of serial sections of each stage. 



Becher, 1907, describes the simultaneous appearance of the three 

 first secondary tentacles in the three dorsal interradii of Ehabdomol- 

 gus ruber, Thompson, 1862, merely states that in Leptosynapta 

 inhserens, at about three months, the sixth and seventh tentacles arise 

 on opposite sides of the circular canal. Baur, 1864, with equal lack 

 of exactness, tells of an eight tentacled stage in Labidoplax digitata, 

 as intermediate between the primary five, and the adult twelve, tenta- 

 cles. Clark, 1898, notes the first five accessory tentacles as appear- 

 ing at the same time in Synaptula hydriformis and agreeing in loca- 

 tion with those of Cucumaria planci as described by Ludwig. The 

 eleventh tentacle arises ventrad from the left, and the twelfth, 

 ventrad from the right dorsal "secondary outgrowth." While Clark 

 does not suggest the homology, it is possible to regard these "sec- 

 ondary outgrowths" as the last vestiges in the degeneration of the 

 protoholothuroid radial canals, thus supporting the phylogenetic theo- 

 ries of Ludwig, 1889-92, and Oestergren, 1907. Ludwig, 1891, 

 does not note an increase in the number of tentacles in Cucu- 

 maria planci until the hundred and sixteenth day, when some of the 

 young animals have the sixth and seventh tentacles dorsad of the right 

 and left ventral radial canals. On the sixteenth day- the primary 

 tentacles develop branches and inaugurate the arborescent form. The 

 same author, 1881, observes that in young Chiridota rotifera, 1898, 

 in Taeniogyrus contortus, and, 1898a, in Phyllophorus urna, two 

 secondary tentacles have arisen, one dorsad from each of the right 

 and left ventral radial canals. Semon, 1883, believes that, in Labi- 

 doplax digitata, the secondary tentacles will prove to be evaginated 

 from the radial canals, at the point where the latter bend over the 

 calcareous ring. Semon emphasizes that his conclusion is theo- 

 retical, and not based on direct observation. 



IV. Pedicels and Papillae. 

 As related above, in Holothuria floridana the first pedicel is found 

 as a bud terminating the posterior end of the mid-ventral radial 



