CRUSTACEANS. 



B. ASELLUS MEDUSAE. Plate LXII. fig. 8. 



Some years ago, I had occasion to make the following entry in my 

 journal, regarding another parasite on the Medusae, which no subsequent 

 opportunity has enabled me to repeat : " Length, half an inch ; antennae, 

 four, long and slender ; two green eyes ; limbs, five pair, besides a false 

 pair ; tail terminating in pieces. It swims swiftly, and its habits somewhat 

 resemble those of the fresh-water Crustaceans. Occurs in September." 



C. CYCLOPS STAGNORUM. Plate LXII. figs. 9, 10, 11, 12, 13. 



From certain points of general resemblance between the preceding 

 animals, and some of the Entomostraca, they ought not to stand very 

 far apart perhaps. The latter are a very numerous race, both marine 

 and fresh-water, many of which having attracted the notice of skilful 

 observers, renders it unnecessary to treat of that special subject in detail. 

 It is chiefly of late that they have become the objects of very minute 

 scrutiny. This will be seen from the works of the Baron de Geer, of 

 Otho Frederick Muller, and particularly, from the copious and very valu- 

 able treatise of Mr Baird, a British naturalist, who, in addition to his 

 own excellent observations, concentrates all the preceding information 

 of others. 



The animals associated as the Cyclopean race, or under the deno- 

 mination of Monoculus, derive their character from Nature having pro- 

 vided them with only a single eye, instead of two or more bestowed on 

 so many of the inferior tribes. Sometimes, indeed, two may be present, 

 so approximated, as to induce the cursory observer to believe that there 

 is only one. 



The nature of vision, its powers, or imperfection, is extremely ob- 

 scure, especially among the tenants of the waters ; some exhibit a single 

 speck, others two, four, or more, or even a profusion which are precipi- 

 tately denominated eyes, without any evidence that they are truly 

 auxiliaries of vision. But we may safely conclude, that their power and 

 their functions are alike equivocal. 



The subject of this paragraph having been noticed by others, I 



