Crustacea of Belgium. 369 



sides ; at each systole these seven faces become strongly con- 

 cave, at each diastole they return to their rectilinear form. 



I have found in Belgium seven species of Daphnia^ a single 

 Bosmina {B. lonqirostn'Sj Baird), and a single Poli/jjhemus (P. 

 oculus, MiilL). The last is excessively rare. 



Copejjoda. — I have made the following observations upon 

 the dermal skeleton. M. Leydig has stated that the cuticle 

 (epidermis) contains no calcareous deposit ; I have demon- 

 strated its presence chemically. The canals which traverse 

 the cuticle in the higher Arthropoda are visible here only at 

 the posterior margin of certain thoracic segments. The 

 material which colours the skin is situated in the soft non- 

 chitinous membrane (corium), and is of a granular nature. 

 The animal probaT)ly lives at its expense during periods of 

 forced abstinence from food ; for, according to my experiments 

 and those of M. Zenker, the colour disappears when the ani- 

 mal is made to fast. The blue or green colouring-substance 

 undergoes no change by the action of bases ; it becomes red- 

 dish by the action of acids, and in this case bases do not bring 

 it back to its original tint. 



The Copepoda are often indebted for other colours to their 

 residence in naturally coloured waters. Following the exam- 

 ple set by B. Prevost with other animals, I put some Cyclo- 

 pidte into water reddened by carmine ; in the course of six 

 days they acquired a rose-colour, and the colouring-matter 

 was to be seen in the digestive tube, in the envelope of the 

 oviferous sacs of the females, and in the interior of the bodies 

 of the parasitic Infusoria. All these observations prove that 

 in this group of Crustacea, notwithstanding the contrary 

 opinion of Midler, colour can never be regarded as a specific 

 character. 



The dermal skeleton of the genera Cyclopsina^ Cantho- 

 camptus^ and Cyclops^ when subjected to the same analysis as 

 that of the DapJinice^ shows six cephalic somites (of which 

 the tergal portions become amalgamated to form a carapace), 

 four thoracic somites, and six abdominal somites, including 

 the telson. The appendicular organs are — a pair of anten- 

 nules, a pair of antennaa, a pair of protognaths, three pairs of 

 maxillipeds, four pairs of thoracic feet or pereiopods (each 

 including an endopod and an exopod), and, lastly, a pair of 

 uropods. 



The muscular system, which is highly developed, merited a 

 careful examination. Histologically the muscles are like those 

 described by M. Leydig in Branch ipus • that is to say, they 

 are composed of a transparent envelope and a contractile sar- 

 code consisting of cuneiform elements closely interlaced. For 



