REVIEW. 289 



5. In green plants, according to Patten, " chlorophyll is without 

 doubt the substance affected, by sunlight," and " the only rational 

 supposition is that pigment is the substance in animals directly 

 affected by the sunlight." It is somewhat impertinent of Dr. Patten 

 to accuse those who may not assent to his crude theories of enter- 

 taining irrational suppositions. Most physiologists will remember 

 that there are not a few simple experiments which demonstrate 

 that protoplasm devoid of pigment is affected by sunlight and by 

 its visible as opposed to its thermal factors. For instance, Engel- 

 manu has shown that the colourless Protozoon Pelomyxa contracts 

 when exposed suddenly to sunlight, and the retina of albinoes is 

 " directly affected " by sunlight. 



6. It is a matter for regret that Dr. Patten has not made himself 

 acquainted with the facts as to th^ action of light on protoplasm. One 

 of the most important lines of inquiry in the minute study of the eyes 

 of Arthropods, Molluscs, and other Invertebrates, is to be found in 

 an exact determination of the presence or absence of pigment in the 

 nerve-end cells and of the distribution of pigment granules in those 

 cells. The question is a difficult one to investigate, because the 

 observer generally is compelled to dissolve the pigment present in 

 an ommataeum before a satisfactory study of the cells can be made. 

 Dr. Patten, in the more valuable portion of his memoir containing the 

 record of his observation, has not given so much attention to this 

 matter as we could wish. It is remarkable that whilst he indulges 

 in such " tall talk " with regard to pigment and heliophagy and the 

 fundamental relation of pigment to this newly discovered function, 

 yet he himself professes (we do not throw doubt on his observa- 

 tion) to have traced the chief optic nerve-fibres of the Arthropod 

 polymeniscous eye to the colourless transparent cells of the 

 crystal cones. It is evidently a subject which does not trouble 

 him much since he quite recklessly attributes to other authorities 

 on Arthropod eyes, statements with regard to the presence or 

 absence of pigment in nerve-end cells which are the reverse of 

 those made by the gentlemen in question. Thus at p. 670 he says: 

 " Let us take for instance one of the lateral eyes of Scorpio and 

 it will be found, according to Grraber and Lankester, that the om- 

 mateum consists of ommatidia each one composed of five central 

 colourless cells or retinophora?." The reader who has followed 

 us so far will not be surprised to learn that the particular cells in 

 question were described and figured by Lankester as pigmented 

 and not colourless, and were made by him the text of a discussion 

 as to the significance of pigment in nerve-end cells. 



7. It is not, however, of any use to expect accuracy of observa- 

 tion as to the contents of books and contemporary memoirs from 

 Dr. Patten. He is far too much engrossed with laying down new 

 principles of physiology and expounding to a benighted world the 

 results of his philosophic meditations. As he himself says (p. 672), 

 since doctors disagree, he intends to choose his own course, picking 



