INTRODUCTION. IX 



the eye than in the adult state. In the genus Gam- 

 marus, the number of lenses in the young is first eight or 

 ten, whilst in the adult they number from forty to fifty. 



The superior or first pair of antennae we consider, con- 

 trary to the opinion of Mr. Dana, to be formed on the 

 same type as those of the Macrura. Each of them con- 

 sists of three distinctly formed joints and a flagellum, 

 with sometimes a more or less important secondary 

 appendage. We have long since expressed our opinion 

 that in these organs lies the seat of auditory consciousness, 

 and we are still inclined to retain that opinion. We are 

 aware of the elaborate experiments of Dr. Von Hensen, 

 which tend to demonstrate the existence of auditory cilia 

 on several parts of the animal, as the superior antennae, 

 (in which Professor Huxley was the first to demonstrate, 

 in some exotic Macrura, the presence of highly refracting 

 otolithes,) on the inferior antennae, as well on the caudal 

 appendages as in the external branch of the posterior 

 pleopoda, on which Van Beneden has discovered, and we 

 have seen, what appear to be well-formed otolithes, of the 

 same type as those found in the first joint of the anterior 

 pair of antennae in Mysis, &c. But we have always 

 attributed to certain very delicate membranous cilia of 

 various forms, found on the primary flagellum only of the 

 superior antennas, and present, under normal conditions, 

 in nearly every family of Crustacea, the power of convey- 

 ing impressions of sound. But these membranous cilia 

 are very distinct from the auditory hairs of Dr. Von 

 Hensen.* 



That the superior antennae are, in their most normal 

 development, purely aquatic organs, we see in the depre- 

 ciation of their character in the partly marine genera 



* An elaborate memoir on the auditory organs of the Crustacea, by Dr. V. 

 Hensen, was published in Zeitschr. f. Wissensch. Zoologie, xiii. Bd. 3. Hft. 

 1863, an abstract of which may be seen in the Zoological Record for 1864. 



