On the Classification of Nemertes and Planarie. AT ; 
not characterize the primary division. It gives but the subordi- 
nate groupings. 
S$ soon as it is acknowledged that the division rests upon the 
structure of the nervous system, the fact that the nervous system 
of Distoma is that of Articulata, and the nervous system of 
' Planarie is that of Mollusca, there is no ground for further 
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hesitation. 
true ; but very apparent towards the posterior region, where they 
are seen sending off smaller threads distributing them to the 
body. 'This arrangement of the nervous system of Distoma be- 
comes especially distinct in Malacobdella where the same arrange- 
ment is found, with the ganglia of the lateral threads more de- 
veloped. Thus, taking the nervous system into consideration, 
_Malacobdella is one degree higher than Distoma, then Clepsine 
would follow in which the two threads are brought so close to- 
gether that they combine into one single thread. Above Clepsine 
would rank the other Hirudines. 
_ In Planarie we have a cephalic ganglion more or less lobed on 
its circumference which sends nervous threads to all the regions. 
There are two more voluminous lateral ones (one on each side of 
the body) asin Distoma, but uniform as in Nemertes, still recalling 
here by analo y the nervous system of Articulata. ‘The funda- 
mental difference, although lest apparent at first sight, consists in 
the absence of ganglia upon their lengths, and this fact decides all. 
he body of Distoma, indeed, is not articulated and this ma 
Perhaps lead to a belief of a closer affinity between Planarie and 
worms. ‘Their broad and flattened form would be better adapt- 
ed to their mode of life without that structure. Moreover the 
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