* 
62 7 On the Classification of Nemertes and Planarie. 
So that the connection although materially expressed, exists es- 
sentially in their immaterial essence. 
Vi. 
I now conclude by a few words on Annelids and Gasteropods. 
Having withdrawn from the first of these classes a certain 
number of its representatives to include them among the second, 
it is to be expected that I should present in a synoptical manner ‘ 
the systematic modifications resulting from it. 
If we admit the two sections of worms proposed by Milne Ed- 
wards, the Pleuronera and Annelids proper, we should place them 
one above the other to form a single series instead of one. 
Opposite we should have the series of Gasteropods beginning 
with Nemertes; above these the Planarizw, then the Nudibran- 
chiata ; 
Annelids proper. Nudibranchiata. 
Annelides, | Seis 
Hirudines. 
Worms. 
Planarie. | ; 
{ 
Peripatus. 
Pines Malacobdella. 
eT Polyeladus 
Helminthes, 
Gasteropods, 
a a 
pel 
| Nemertes. | ee RE Boe 
| 
simple reason that embryology assigns a lower rank to all Gaste- 
ropods provided with a shell, inasmuch as Nudibranchiata, when 
hatched, have a shell, which they lose at an early period of their’ 
life. ‘Phe attempt at forming organic series in the animal king- 
tive value. Unless several series are established in the class of 
Gasteropoda, the position of Nudibranchiata in the above synop- 
sis cannot be accounted for. I have already made the remark 
that Planariz were rather parallel to Nudibranchiata than of a 
lower rank, finding in these two families groups of equal im- 
portance, 
*The natural relations between Animals and the Elements in which they live; 
by Prof. L. Agassiz. This Journal, 2d ser, vol. ix, p. 369. . 4 
