1901.] NATURAL SCIENCES OF PIIILADELPHIA. 729 



system and cerebral sense organs, and of the proboscis; while the 

 affinities with the Protonemerteans — and certain Heteronemerteans 

 — are in the absence of lateral slits, in the presence of an inner cir- 

 cular muscle layer and of crosses between this layer and the outer 

 circular, and in the lateral grooves, if souse organs. 



The general simphcity of its Heteronemertean structure and the 

 several Protonemertean characters bring Zijgeiqjolia very near to 

 the Protonemerteans, and through Zygeupolia the whole Hetero- 

 nemertean ordex is more closely connected with the Protonemer- 

 teans. 



The question now arises, To which of the families of the Hetero- 

 nemerteans does Zygeupolia belong — to the Eupoliida?, or to the 

 Lineidie ?'* 



The chief characteristics of the two families Avill now be giv^en, 

 according to Biirger (1895): 



The Eupoliidce. — (1) No lateral slits in the head, the cerebral 

 canal opening directly outward or into shallow ventral furrows. 



(2) No muscular crosses in the proboscis. 



(3) The proboscis musculature consists of two layers, an outer 

 circular and an inner longitudinal muscle layer. 



(4) A head gland is prominent, the gland cells reaching back 

 into the oesophageal region. 



The Lineida'. — (1) The canal of the cerebral organ opens 

 usually, not directly outward, but into deep, or sometimes shallow, 

 lateral slits in the head." 



(2) Two muscular crosses in the proboscis. 



(3) The proboscis musculatur consists of three layers — longitu- 

 dinal, circular and longitudinal muscle layers; if any one of these 

 layers is absent it is the inner longitudinal one. 



(4) The head gland is represented by a few gland cells, and 

 does not extend posterior to the brain. 



^^In my preliminary note upon ZygenjJoUa ''1900 a) this genus is placed 

 in the Enpoliidse, on account of the absence of lateral slits and the supposed 

 absence of muscular crosses in the proboscis. As I have since found muscu- 

 lar crosses in the proboscis, I wish to correct this error. 



" Biirger's own words in regard to the lateral slits are here given (1895, 

 p. 613): ''Der Canal des Cerebral organs miindet in der Kegel nicht direct 

 nach aussen, sondern in tiefe laterale hoiiznntale Taschen, welche durch die 

 Kopfspalten gebildetslnd. Die Kopfspalten sind wechselnd tief : sie schnei- 

 den haufig bis auf das Hirn ein, aber sie sind auch, obwohl in seltenen 

 Fallen, nur durch flache laterale Langsbuchten angedeutet." 



