334 On the Variations of certain Crustacea. 



Some northern species are, at Nice, represented by very 

 nearly related forms. Thus the northern Dactylopus Stromii, 

 gives place to D. similis ; the northern Harpaticus chelifer to 

 27". oiicceensis. Similar differences may be noted between the 

 Gopepoda of Nice and Messina, the species and genera of which 

 places are for the most part the same, and, in many cases, of 

 invariable form, e. g., Euchceta Trestandrem, and Gandace 

 melanops. But there is a constant deviation observed in 

 Galanus mastigophorus. 



The most important distinctive characters met with 

 amongst the Gopepoda are in the size and colour of the 

 body, the form and length of the tail, the form and number 

 of joints of the upper antennae, the character of their appen- 

 dages, the character of the eyes, etc. The colour of a 

 species may, however, be due to the distribution of pigment 

 in various form through the external tissues of the body, or 

 it may result merely from masses of food lodged in the 

 alimentary canal, or from the natural colour of organs such 

 as the ovaries. Indeed, it is often very difficult to decide 

 how far in particular cases variations of colour may depend 

 upon outward conditions, such as those of food and tem- 

 perature. 



It is worthy of remark that some very common species 

 have a large and a small variety, and that we do not find 

 intermediate sizes. These may, perhaps, exist, but they 

 are seldom seen. Thus a large form of Dactylopus similis 

 is 1'2 mm. in length, the small variety only 0"7 mm. Tisbe 

 furcata also varies at Nice from 1*4 mm. to 2"3 mm., and there 

 is a form of Antaria mediterranea, in which some of the middle 

 segments are wholly, or in part, wanting. As connected with 

 this part of the subject, I may note that I find a variety of 

 Diets longiremis in brackish water at Burgh Marsh, Cum- 

 berland, also in similar situations at Hartlepool and Alnmouth, 

 the length of which is only one-thirty-fifth of an inch, that of 

 the normal form being one-twentieth of an inch. 



The characters of the tail setas, and the joints of the 

 antennas are of great specific importance amongst the Copc- 

 poda, and there are many striking variations in these respects, 

 as, for instance, in Gyclops serrulatus, Antaria mediterranea, 

 and various Gorycei. Differences in the size of the various 

 joints of the antennas are very common. In Ha/rpacticus 

 nicosensis the third and fourth joints are often much elongated; 

 in a large variety of Tisbe furcata, the size of each joint is 

 subject to much variation ; and there is also a vai-iety of this 

 species which bears a very large secondary branch on the lower 

 antenna ; the terminal joint being excessively elongated. In 

 Dactylopus similis the fifth and sixth joints are very variable, 



