PART I. 

 THE CLASSIFICATION OF THE APODOUS HOLOTHURIANS. 



The first writer on Holothurians who recognized the presence or absence 

 of feet ( pedicel sj as an important character in the classification of the group 

 was J. F. Brandt ('35), in his account of the animals observed by H. Mertens. 

 He divided the group Holothurine, which he ranked as a family, into two great 

 subdivisions, the PEDAT.E and the APODES. Unfortunately, however, he failed 

 to distinguish accurately the apodous from the pedate forms, and conse- 

 quently, as Ludwig ('Sib) has shown, many really apodous forms occur in the 

 Pedate. He divided the Apodes into the PNEUMONOPHORE and the APNEU- 

 MONES, according to the presence or absence of respiratory trees. But here 

 again his observations were not exact, and some forms without respiratory 

 trees are placed in his Pneumonophora?. Burmeister ('37) ranked the holothu- 

 rians as an order including several families, one of which, called by him SYN- 

 APTID.E, was equivalent to Brandt's Apodes. Grube ('40) called the same group 

 CHIRIDOTJE, Forbes ('41) called them SYNAPT^E, Gray ('48) SYNAPTIDJE, and 

 Siebold ('48) SYNAPTIN.E. Johannes Miiller ('50) considered the possession of 

 respiratory trees as the important point in holothurian anatomy, and accord- 

 ingly he divided the order into "lungenlose" and " lungentragende " groups; 

 the latter were divided into the "fusslose" and "fussige," and the "fusslose" 

 were christened MOLPADIID^E. Bronn ( '60) recognized the position of the holo- 

 thurians as a class, and divided it into two orders, the first of which contained 

 only the extraordinary Khopalodina, while the second was divided into two sub- 

 orders, APODIA and EUPODIA, the Apodia equivalent to Brandt's Apodes. Under 

 the APODIA were placed two families, the Synaptidae (without respiratory trees; 

 four genera, Synapta, Synaptula, Chiridota, Myriotrochus) and the LIODER- 

 MATIDJE (with respiratory trees; three genera, Lioderma, Haplodactyla, Mol- 

 padia), Miiller 's Molpadiidas. 



With the publication of Selenka's monograph ('67) the study of the holo- 

 thurians really began, from a modern systematist's point of view. He divided 

 the class HOLOTHURIOIDEA into two orders, the PNEUMONOPHORA and the Ap- 

 NEUMONA, the former with three families, the last of which, the LIOSOMATIDJE, 

 was equivalent to Miiller 's Molpadiida?. Selenka's classification of the footless 

 forms may be tabulated thus : 



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