200 LAKE SUPERIOR. 



require that we introduce Bryozoa among Acephala and place them 

 lowest in that class, next the compound and simple Ascidige, and then 

 the Brachiopoda and true Acephala. Among Gasteropoda I would 

 introduce Foraminifera as their lowest type, exemplifying, in a perma- 

 nent condition, the embryonic division of their germ, next the Ptero- 

 poda would follow, also as an embryonic form of Gasteropoda, in 

 which the lateral fin-like appendages and the symmetrical shell remind 

 us of the deciduous shell of naked Gasteropoda with their vibrating 

 wheels, and next the Heterobranchia, the common branchiferous Gas- 

 teropoda, and uppermost the Pulmonata, in some of which the embryo 

 is not even aquatic, nor provided with fringed appendages. As for 

 the Cephalopoda, I have recently had sufficient evidence from em- 

 bryonic investigations that the Octocera stand below Decacera. 



