MOLLUSCS AND BRACHIOPODS. 



439 



instance, for those who have not had any special training, and 

 who are not necessarily acquainted with scientific language. At 

 the same time, an attempt is made, not only to combine popular 

 treatment with the latest results of scientific research, but to make 

 the volumes useful to those who may be regarded as serious 

 students in the various subjects. 



The general plan of classification adopted in the work before 

 us is not that of any single authority. It has been thought better 

 to adopt the views of recognised leading specialists in the various 

 groups, and thus place before the reader the combined results of 

 recent investigation. 



Fig. I, — Eye of Helix pomatia, L., 

 retracted within the tentacle ; c. , cornea ; 

 ej>. , epithelial layer ; /. , lens ; op. n. , 

 optic nerve ; r. , retina. (After Simroth). 



'^cpji 



The volume opens with a Scheme of the Classification of the 

 Mollusca adopted in this book ; followed by chapters on the Posi- 

 tion of Mollusca in the Animal Kingdom ; Origin of Land and 

 Fresh-water Mollusca ; Their Habits and General Economy ; 

 Their Enemies ; Means of Defence, etc. etc. 



As the publishers have very kindly placed some of the illustra- 

 tions at our disposal, we will now pass on to Chapter VII., which 

 treats of the Organs of Sense: Touch, Sight, Smell, Hearing; 

 The Foot and the Nervous System, and quote briefly — 



The Organisation of the Molluscan Eye (p. i8i). — The eye in 

 Mollusca exhibits almost every imaginable form, from the extremely 

 simple to the elaborately complex. It may be, as in certain 

 bivalves, no more than a pigmented spot on the mantle, or it may 



