lii Journal of Comparative Neurology. 



eral nerves, 7 to nerve cells, and 5 to spinal cord, cerebellum and cere- 

 brum. Mechanically the book is badly constructed. The binding of 

 blank pages of ordinary book paper into a laboratory guide for the stu- 

 dent's drawings is a practice not to be recommended. It is our expe- 

 rience that much better results are secured by the use of tablets of good 

 drawing paper properly punched so that they can at the end of the 

 course be bound up in any desired order by the student. Even if the 

 guide is interleaved with good drawing paper, this arrangement is 

 inconvenient and otherwise objectionable. 



c. J. H. 



The Eyes of Decapods. ' 



Investigations on the invertebrate nervous system have of late 

 scarcely kept pace with the phenomenal advances made in the domain 

 of the vertebrates. This of course is largely due to the enormous diffi- 

 culties encountered in the development of an appropriate histological 

 technique. It is therefore with considerable interest that we watch the 

 result of each new attempt to apply to the various tissues of the inver- 

 tebrates the modern methods which have made possible the great dis- 

 coveries of the last decade in vertebrate neurology. This mono- 

 graph by Dr. Parker brings into prominence very vividly the great 

 fruitfulness of this field when it is cultivated by one who has the 

 patience and ingenuity necessary to overcome the mechanical difficulties 

 of the research. In these days when the hterature is made up so 

 largely of the immature productions of callow students and of prelim- 

 inary notices of observations which are never verified it is a grateful 

 relief to meet with a study so thoroughly and symmetrically executed 

 as this one. 



It is impossible to give an adequate abstract of the paper without 

 reference to the accompanying plates ; a few only of the author's con- 

 clusions are therefore presented. The methods which yielded the most 

 valuable new data were those of Golgi and Ehrlich ( methylen blue). 

 A valuable feature is the systematic counting of all the elements of the 

 eye and ganglion which could be made available for the purpose. The 

 fibres of the rhabdome are regarded as nervous structures, the distal 

 ends of the fibrillse of the retinal nerve fibres. Each retinula is made 

 up of seven elements, each of which represents a single cell which is a 

 neuron in the sense of Waldeyer. The details of the structure of the 

 rhabdome are presented with great distinctness. The pigment was 



^Parker, G. H. The Retina and Optic Ganglia in Decapods, especially 

 in Astacus. Mittheilungen a. d. zoologischen Station zu Neapel, XII, i, 1895. 



