562 



DOUTDIDiE. 



This and the two following families constitute the order 

 NuDiBRANCHiATA of Cuvier. The Molhisca they include 

 are entirely destitute of shells, except when in the embryo 

 state. Their branchial organs are constantly external, and 

 are variously arranged along the margins or on the dorsal 

 surface of the body. The individuals are hermaphro- 

 dite. In the DoRiDiDj^ the branchial plumes are placed 

 on the middle of the back, in immediate proximity with 

 the vent. 



Since the chief intention of this history is to describe 

 and figure fully the testaceous molluscs of the British 

 islands, more especially the marine tribes, at the same time 

 that we give a summary of the species unprovided with 

 shells, our account of these nudibranchous orders must 

 necessarily be extremely brief. To treat of them in detail 

 would be to extend our volumes far beyond the proposed 

 bounds. Fortunately, there is no necessity for doing so, 

 since one of the most beautiful and perfectly executed 

 works of which zoological science can boast, is devoted to the 

 British Nudibranchiata. We allude to the Monograph by 

 Messrs. Alder and Hancock, published by the Ray Society. 

 The figures and descriptions (the language of which we 

 have closely followed) contained in that treatise are beyond 

 all praise. To them we must refer those of our readers 

 who desire to master this interestinof branch of studv. 



