82 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



made up of forms presenting widely divergent anatomical pecul- 

 iarities and is now looked upon as a very heterogeneous group. 



Further division of this grou]) was made by Hubrecht who, in 

 1879, established the order Hoplonemertea as equivalent to the 

 Enopla of Max Schiiltze and divided the Anopla into the order 

 Schizonemertea, or those forms having a pair of deep lateral longi- 

 tudinal cephalic furrows, and the Paleonemertea, including all other 

 forms which are without proboscidial stylets and T\'ithout lateral 

 cephalic furrows. 



Further anatomical studies, however, have shown that the pres- 

 ence of cephalic furrows is a very artificial distinction, for genera 

 showing great correspondence in their principal anatomical pecuhar- 

 ities, as Taeniosoma and the Lineidae, are thus placed in different 

 orders, while! widely divergent forms, differing profoundly in 

 arrangement of muscular layers and position of lateral nerves, are 

 brought together in one order. With the recent discovery of 

 Zygeupolia and several other forms undoubtedly belonging to 

 the Lineidae but without lateral cephalic furrows the objection to 

 Hubrecht's classification becomes still more obvious. 



Biirger, in 1892 and 1895, proposed to divide the nemerteans into 

 four orders distinguished by fundamental anatomical peculiarities 

 such as the number and arrangement of the muscular layers of 

 the body, position of lateral nerves, and structure of proboscis. 

 The more important characters of these four orders are as fol- 

 lows : 



I. Protonemertea. Brain and lateral nerves situated in the epithe- 

 lium or beneath the basement layer outside the body musculature, 

 which is made up of two layers, often with diagonal fibers between 

 them ; mouth situated behind brain ; intestinal caecum and stylet 

 apparatus absent. 



II. Mesonemertea. As in the Protonemertea, except that the 

 brain and lateral nerves lie imbedded in the body musculature. 



III. 3Ietanemertea. Brain and lateral nerves situated in the par- 

 enchyma internal to the body walls ; mouth in front of brain ; 

 intestinal caecum and stylet apparatus present. Corresponding both 

 with the order Enoi)la of ]Max Schultze and that of Hoplonemertea 

 of Hubrecht. Malacobdella is placed in this order by Burger, 

 although, as stated below, it differs so widely from all other genera 

 as to warrant the establishment of a distinct order for this genus 

 alone. 



