PYCNOGONIDA. 



Linne: cauda; O. Fabricins: caiida; Latreille: le dernier segment du corps; Lamarck: 

 abdomen; Leach: abdomen; Savigny: abdomen; Johnston: abdomen; Milne-Edvards: abdomen; 

 Erichson: Hinterleib; Kr0yer: Bagkrop, abdomen; Wilson: abdomen; Dohrn: Hinterleib; 

 B0hm: Abdomen; Hoek: abdomen; Adlerz: abdomen; Han sen: Bagkrop (abdomen); Sars: Hale- 

 segment (segmentum candale). 



The appellation of this part of the trunk was in the early authors (Linne and O. Fabricius) 

 simply cauda, tail; but Latreille having pointed out that it was a part, a segment, of the trunk 

 itself, the first name was displaced by the appellation abdomen and the translations of it (Hinterleib, 

 Bagkrop), which was adopted by all authors until Sars, the opinion being, I suppose, that it corre- 

 sponded to the abdomen of the other Arthropoda, especially that of the Insects and the Arachnida. 

 Sars, as it were, has meant to adopt the old name of tail, but on accoiint of the prevalent aversion 

 to this appellation, he has altered it to the mediate one of caudal segment, and I have followed him 

 partly of similar reasons. -- As to its development the caudal segment is the hindmost part of the 

 hindmost principal division of the embryo, and until a far advanced stage in the larval development 

 it forms a hindmost, gradually more protruding, process of the fourth segment of trunk. If upon the 

 whole it is separated from this segment by a dermal suture, this does not take place until the third 

 larval stage. It never bears limbs, but the intestinal canal opens in the end of it with a weak squir- 

 ting apparatus. Thus the caudal segment no doubt belongs to and makes the hindmost 

 part or segment of the same principal portion to which the four preceding segments 

 belongs; it is no separate part of the body, different from the foregoing segments of the trunk, no 

 abdomen in contradistinction to a thoracical part, lying before it. The caudal segment can be pro- 

 portionally very long, almost as long as the body, and then it is also well separated from the fourth 

 segment of the trunk and very slender; there is no trace of division in joints, not even in Zetes 

 (Eurycyde\ as has been maintained. On the other hand this segment may also be quite small, as it 

 were, rudimentary, as I know from a not described genus among the collections, which the Smithsonian 

 Institute has given me for examination. 



Lateral process of the body for the insertion of the ambulatory legs (process us 

 corporis lateralis), fig. i pel. 



Sars: Legemets Sidefortsatser (processus laterales corporis) til Faeste for Gangfodderne. 



These processes of the body and the ambulatory legs attached to them, are structures charac- 

 teristic of the Pycnogonida, as they are not formed by germinating or growth of a particular cellular 

 group but, as is distinctly seen from my drawings of the embryo, by a bag-like constriction of the 

 ectoderm, in the same manner as the embryonal limbs (the chelifori and embryonal legs). They are 

 in reality only parts of the body, and so it will easily be imderstood, that the intestinal canal and 

 the sexual glands can continue far into the ambulatory legs as processes of the bod}-. 



Ch el if or us (chcliforus\ fig. i chf and 2 a. 



Linne: palpi; O. Fabricius: palpi; Latreille: mandibxiles; later (Regn. an. ed. II) : antenne- 

 pinces; Leach: mandibulse; Savigny: pedes secundi; Lamarck: antennules; Johnston: mandib- 

 les; Milne-Edwards: pattes-machoires ; Erichson: erstes Kieferpaar or Scherenkiefer (Mandibeln); 

 Kroyer: Saxe (antennae cheliformes); later Kindbakker (mandibulse) ; B0hm: Kieferfuhler ; Wilson: 



