CRUSTACEA. 323 



Tenaclt}'- of life in the Crustacea appears not to be enjoyed in any 

 unusual degree : but some species, as the Artemia salina, can exist 

 in hot and strong brine, which would quickly destroy most other 

 animals. This shrimp abounds in the brine-pans of the Lymington 

 salt-works. 



Like other Articulata subject to periodical ecdysis, the Crustacea 

 have the power of reproducing lost extremities. If a leg be frac- 

 tured across one of its segments, it is cast off by a violent muscu- 

 lar effort : if the Crustacean have not the power of thus ridding 

 itself of the wounded member, it usually dies from the haemorrhage ; 

 otherwise this is immediately arrested by the contraction of the 

 lacerated part of the joint where the limb is cast off with least dif- 

 ficulty and pain. The pre-arranged place of easiest and safest sepa- 

 ration is close to the basal end of the first joint, along a transverse 

 ciliated groove. This joint is filled by a mass of nucleated cells, 

 surrounded by a vascular band. The vessels of the band pass half an 

 inch beyond it, and return upon themselves forming loops. The 

 reproductive cells multiply after the loss of the limb, and form five 

 masses, which are the rudiments of the five joints of the future 

 limb: this, in the crab, is folded at the first joint, but is extended in 

 the lobster : in both it is enveloped in a sac or dilated cicatrix, which 

 the young limb, as it grows, bursts ; and it then resembles in minia- 

 ture the limb which it is destined to replace : its growth is slow until 

 the j)eriod of the moult, when, if the animal be in vigorous health, 

 the ne-w member rapidly acquires its normal size. 



Generation of the Crustacea. — With regard to some of the smaller 

 Entomostraca, only the females have hitherto been discovered ; and 

 some naturalists have endeavoured, as in the case of the Aphides, to 

 solve the phenomena of parthenogenesis in such Entomostraca by- 

 alleged gynandrism. Thus, in the genus Apus, the lamelliform 

 respiratory sacs which, after death, get distended with blood, as 

 Siebold has shown *, were described by Berthold to be the testes co- 

 existing with ovaria, which are large and conspicuous. Again, in 

 the "genus Cypris, Straus-Durkheim t points out, in addition to the 

 ovaria, a pair of sacculi at the fore-part of the stomach ; but, with his 

 usual philosophic caution, doubtfully alludes to their nature as either 

 testes or salivary glands : they appear to me to be homologous with 

 the caBca in the Daphnia, which most comparative anatomists have 

 agreed in determining to be the liver ; there is no other part that 

 could be mistaken for a male organ. 



In the genus Daphnia the males are well known ; they are 



* XXIV. p. 484. t CCXXXIV. p. 384. 



Y 2 



