ZOOLOGY. 437 



cause acting through the habits of the animal after it lins 

 passed through its zoea stage. Alpheus is a parallel ease, 

 and as the result has been somewhat similar, it is highly 

 probable that the conditions have been parallel. Alpheus is 

 in the young stage a free-swimming animal with powerful 

 organs of vision, but in its adult condition it burrows in 

 sponges, etc., where the eye is of little use. Willemoesia also 

 in its young stage has well-developed eyes, which it loses 

 when it has arrived at its adult condition. This, the writer 

 thinks, is attributable to a similar cause, viz., that it burrows 

 in the soft mud of the deep-sea bottom. That the imperfect 

 state of the eyes is not due to the loss of light from the great 

 depth at which "W-illemoesia is taken is evident from the fact 

 that Thalascaris (a new genus of Crangonidce) is taken at 

 depths equally great, and is remarkable for the large size of 

 its eyes. 



In a report on the present state of our knowledge of Crus- 

 tacea, Mr. Spence Bate gives a resume of what is known of 

 the ears of these animals, especially the shrimps and crabs. 

 From experiments made by Dr. Hensen, it appears that crabs 

 and shrimps living in water did not notice sounds made in 

 the air, and that they were only slightly affected by sounds 

 made with a fife or bell in contact with a membrane connect- 

 ing the same witli the w r ater. In experiments made with 

 musical notes, he found that certain hairs vibrated to certain 

 sounds. Under these conditions, Dr. Hensen found that a 

 certain hair, which only vibrated under one note, will, under 

 a different one, shake to the very base so powerfully that it 

 cannot be distinctly observed, and that as soon as the sound 

 ceases the movement also ceases. He has accordingly drawn 

 up a scale of musical notes adapted to the various hairs which 

 he thinks belong to this sense. 



The structure of the eyes of worms and Crustacea has been 

 carefully studied by J. Chatin, whose results appear in the 

 Ann. des Sc. N'aturelles. He concludes that the staff or fila- 

 ment of the optic nerve forms the most important part of the 

 elements of the eye. Limited externally by the cornea, con- 

 fined internally to the ganglion of the optic nerve, the staff 

 consists of two parts quite distinct, differing notably in char- 

 acter and value; one being internal, and more or less slen- 

 der, which should be called the staff or batonnet (literally 



