22 SENSIBILITY. 



such animals are brainless as well as headless. Pteropods con- 

 stitute a kind of link, leading us from comparatively sluggish 

 Lamellibranchs to Gasteropods and Cephalopods, organisms 

 possessing distinct heads with sense-organs, and more or less 

 developed brain. The nervous system of the Gasteropods is 

 better developed, more complex, and concentrated. The Cepha- 

 lopods stand considerably above all other Molluscs, the sensory 

 organs being developed to a high degree. 



Nothing distinctly answering to a brain is to be found in many 

 of the lower animals in which nervous systems exist. Thus, in 

 the Star-fish and large Nematoid Entozoa, what most resembles 

 such an organ consists of a mere band of nerve-fibres surrounding 

 the commencement of the oesophagus. Among the representa- 

 tives of the sub-kingdom Vermes^ the nervous system varies a 

 good deal in minor details. The broad features are, however, 

 comparatively similar in all. 



Without pursuing the subject as to detail, we have said quite 

 sufficient to show how interesting are the steps which lead from 

 the simple forms of sensibility on to its most complex stages ; 

 and perhaps at some future time we may attempt to deal with 

 the other aspects of this very fruitful branch of psychological 

 science. 



Those who have used the paraffin embedding method for 

 serial sections have, doubtless, wished for some simplification of 

 the process of staining. This may be done, according to 

 Dr. Kiikenthal, by dissolving the colouring matter in absolute 

 alcohol and dropping the solution into turpentine until the desired 

 depth of colour is secured. Sections fixed to the slide with the 

 collodion are kept in the oven until the clove-oil has completely 

 evaporated, the paraffin dissolved in turpentine as usual^ and the 

 slide brought into the dye. The staining is quickly effected. 

 Overstaining may be corrected by placing the slide for a short 

 time in a mixture of acid-free, absolute alcohol and turpentine 

 (equal parts). Turbidity of the colouring fluid may be corrected 

 by adding a drop or two of alcohol. Meyer's carmine, methyl- 

 green, methyl-blue, gentian violet, safranin, eosin, fuchsin, tropaeo- 

 lin, and malachite-green may be used in the above way. 



