1909- Reviews ' 133 



REVIEWS. 



CRABS, LOBSTERS, AND THEIR ALLIES. 



A Treatise on Zooloi^y. Edited by Sir Ray Lankkster, K.C.R., 

 LL.D., F.R.S. Part vii. Appendiculata (third fascicle), Crustacea 

 by W. T. Cai^man, D.Sc. Ivondou : A. and C. Black, 1909, pp. viii. 

 + 346. Price T5J-. net. 



No one can fail to be impressed by the thoroughness which characte- 

 rizes this scholarly work. Dr. Caiman has accomplished the difficult 

 task of furnishing us with an excellent treatise on the structure and 

 classification of the Crustacea. To the ordinary Irish reader who has 

 been accustomed to regard William Thompson as the one great native 

 naturalist, and who has scarcely heard of J. Vaughan Thompson of Cork, 

 this book wall be revelation. Though not a popular writer like his 

 northern namesake, the latter has the distinction of being the first 

 zoologist to place the crustacean nature of the so-called acorn-shells 

 (Cirripedia) beyond dispute. He was the first, also, who drew attention 

 to the phosphorescence of certain crustaceans. Altogether, his many 

 original observations on marine invertebrates place J. Vaughan 

 Thompson among the foremost naturalists of the early part of last century. 



Apart from the fact that the Cirripedia, to which the acorn-shells 

 belong, have attracted attention from the time of Aristotle, their sessile 

 nature in the adult stage while the young are free-swimming, their 

 structural differences from typical Crustaceans, and the most remarkable 

 sexual dimorphism exhibited by some of them, have always caused a 

 lively interest to be taken in them. In most of the Cirripedia, moreover, 

 the individuals of a species are similar and hermaphrodite. In the two 

 genera Scalpellum and Ibla however, dwarf male individuals occur. 

 The latter are attached within the mantle-cavity of the larger individuals. 

 When these are hermaphrodites, the dwarf males pair with them, thus 

 presenting a most curious and unique condition. 



The change from a free-swimming to a sessile condition with a corres- 

 ponding modification in structure is carried even further among those 

 species which eventually become purely parasitic. In Sacculina we 

 possess one of the most striking instances of such a modification to be 

 found in the whole Animal Kingdom. The larva is hatched out as an 

 active free- swimming nauplius. A few days after it becomes attached to 

 a crab, undergoing a remarkable metamorphosis within the body of the 

 latter. The adult Sacculina re-appears on the abdomen of the crab as a 

 simple sac without traces of segmentation, limbs, or alimentary canal, 

 taking its nourishment by means of root-like processes from the body of 

 the host. Of especial interest is the phenomenon lately investigated by 

 G. Smith, that the infected male crabs, in various degrees, assume the 

 secondary sexual characters of females. 



