414 Mr. L. J. Cole on Ten-legged Pycnogonids. 



the acceptance of the homologies of the metameres and ap- 

 pendages of the Pycnogonidaassugu^ested l)y Lankester (1904), 

 who beheves that the whole portion of these animals anterior 

 to the so-called al)domen corresponds to the prosoma of the 

 Arachnids. The scffment which heai*s the fourth pair of 

 ■walking-legs he thinks represents the pregenital somite, and 

 it is true that wherever else the genital openings may be 

 wanting, they appear alM-ays to be present on this pair of 

 legs. Neither Eights nor Hodgson mentions the genital 

 openings in the ten-legged forms, and a knowledge of con- 

 ditions there will be of considerable theoretical interest. It 

 may be mentioned here that Lankester appears to have over- 

 looked the two pairs of appendages present in the embryos of 

 all Pycnogonids (possibly absent in Pallene and related 

 species : INleinert, 1899), which are not represented in the 

 appendages of any adult species. Lankester considers the 

 Pycnogonida a subclass of the Arachnida, and Mcinert, 

 chiefly from his studies of the embryology, also relates them 

 to that group, but differs entirely from Lankester in his 

 conception of the homologies of the various appendages. 

 Carpenter (1903) likewise classes them with the Arachnida 

 and agrees more nearly with Lankester as to the homologies 

 of the metameres; he believes, however, that the palps of 

 the Pycnogonids are not represented by appendages in living 

 Arachnids, and concludes that the present type of Arachnid 

 head *•' was preceded by a head with four pairs " of ap- 

 pendages. More recently Mcisenheimer (1902) has made a 

 careful study of the early embryonic stages of Ammothea 

 echinata, and has reached conclusions exactly opposed to 

 those of Meinert. In a short paper giving his main results 

 Mcisenheimer (1902 a), after presenting his evidence, con- 

 cludes (p. 64) : — "Und somit hat uns die Larvenentwicklung 

 der Pantopoden mit grosser Bestimratheit auf eine nahe 

 Yerwandtschaft dieser Gruppe mit den Crustacean hinge- 

 fiihrt." It is thus obvious that naturalists are no nearer to 

 agreeing to-day upon the systematic position of the Pycno- 

 gonida than they have been at any time iu the past. 



Cambridge, Mass., U.S.A., 

 12th Jauuary, 1905. 



List of Papers referred to. 



Cabpenter, G. H. 



(1903) " On the Relationship.9 between the Classes of the Arthrnpoda." 

 Proc. Roy. Irish Acad. vol. xxiv. sect. B, pt. 4, pp. 320-360, 

 pi. vi. 



