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KINGSLE V. [Vol. \' 1 1 1. 



layer in the body wall; the absence of striation from all muscles 

 except those of the mouth parts; the presence of cilia in the 

 alimentary canal and in the nephridia; the situation of the 

 antennse as outgrowths from the primitively preoral region {cf. 

 supra p. 232); the muscular nature of the pharynx, unlike that 

 of any Arthropod and strikingly like that of certain Chaetopods. 

 The eyes too are unlike the visual organs of any other Arthropod 

 but as figured by Balfour they closely resemble these organs in 

 Autolytus. It is noticeable that Balfour has described ('83) a 

 pair of problematical organs upon the lower surface of the 

 brain of P. capcnsis (the auditory organs of Grube, '53). Sedg- 

 wick has shown that these organs are developed by an invagin- 

 ation of the cerebral surface while the slight account given by 

 Balfour of the adult structure at once suggests a degenerate 

 eye formed upon the same plan as the functional one. In 

 Autolytid worms a second pair of eyes occur at the same point. 



On the other hand the Arthropod structures are not to be 

 ignored; the tracheae; the appendicular jaws; the setting aside 

 of a pair of nephridia for genital ducts; the heart, with several 

 paired ostia, enclosed in a pericardium; the lacunar circulation, 

 and the reduced coelom. 



To the discussion of the position of the Pycnogonids and 

 the Tardigrades I can add nothing. Morgan ('9o) has, it seems, 

 shown that the Pycnogonids present certain features both in 

 ontogeny and in adult structure which can only be paralleled in 

 the Arachnids, while the Tardigrades may have no other claim 

 upon a position in the same group than that afforded by their 

 eight ambulatory feet. 



For many years the general consensus of opinion has been 

 to the effect that the Trilobites are closely related to the 

 Xiphosures. We unfortunately know but little regarding the 

 structure of the Trilobites aside from the features presented by 

 the dorsal surface. For our knowledge of the appendages we 

 have to thank the papers of Billings ('70) and Walcott ('81 and 

 '84). From Billings' paper (and from electrotypes of his 

 specimens which I have studied) we can learn but little except 

 the presence of jointed appendages. Walcott's researches 

 tell much more, but the facts which they have added all are 



