186 



CRYPTANDRA. 



quite sufficient to render their separation permanent. 

 It may also be observed that the changes presented 

 to our notice in the Crustacea, are quite peculiar, and 

 of a totally different description from those of insects." 

 Mr. Thomson then proceeds to notice the different 

 extraordinary animals known to naturalists under the 

 name of zoea. which, from their peculiar structure, 

 had greatly perplexed systematic crustaceologists, 

 and states, " It will no longer be a matter of surprise 

 that all the leading naturalists of the present day 

 should have been at a loss how to dispose of zoea in 

 their arrangements of the~crustacea, when it is known 

 that this singular type is not a perfect animal, but 

 merely the larva or imperfect state of the crab ! and 

 not as had been imagined an animal sni generis." 

 Subsequently our author states, amongst other circum- 

 stances, that he, " succeeding in hatching the ova of 

 the common crab, during the month of June, which 

 presented exactly the appearances of Zoea Taurus, 

 with the addition of lateral spines to the corselet, the 

 Crustacea then indisputably undergo a metamorphosis, 

 a fact which will form an epoch in the history of this 

 generally neglected tribe, and tend to create an 

 interest which may operate favourably in directing 

 more of the attention of naturalists towards them*." 

 And as the zoeas are aquatic animals furnished with 

 swimming organs, Mr. Thompson concludes that the 

 circumstance of the young of the Crustacea being thus 

 natatory, enables us satisfactorily to account for the 

 annual migration of the land crabs of the West 

 Indies to deposit their eggs in the water. We have 

 thus given Mr. Thompson's observations at some 

 length, because the facts, if fully established, are 

 highly interesting, and sufficient to raise Mr. Thompson 

 to a very high rank amongst naturalists. It is pro- 

 per, however, to state, that Dr. Rathke has, in a series 

 of microscopic observations, far more elaborate than 

 any hitherto published by Mr. Thompson, clearly 

 shown the gradual development of the cray-fish within 

 the egg, and which, upon bursting into life, possesses 

 all the form of its parent, whilst the Rev. Lansdown 

 Guilding has expressly stated that the land crabs do 

 not undergo any metamorphosis (Mag. Nat. Hist., 

 May, 1835), a statement which we can fully confirm ; 

 thus, two examples in the great divisions of Brachyura 

 and Macroura are shown to militate against Mr. 

 Thompson's assertion, that the Crustacea universally 

 undergo metamorphosis ; and, as the organisation of 

 those two animals is so completely analogous to that 

 of the common crab (the young of which Mr. Thomp- 

 son affirms to be a zoea) and the rest of the Decapoda, 

 we think that analogy strictly warrants us in assuming 

 that Mr. Thompson must have fallen into some 

 fundamental error in his observations. We look 

 forward, with great interest, to his promised continu- 

 ation of these memoirs, which have been too much 

 neglected by naturalists. 



Various "modes of distribution of this class hare 

 been proposed by different crustaceologists, which it 

 would occupy too much space to detail ; we shall, 

 therefore, proceed to give a short sketch of that 

 which appears to us to be the most natural hitherto 

 published, namely, that by Latreille in the second 

 edition of the Regne Animal, premising only that we 

 have omitted the fossil tribe of Trilobitcs, which will 

 form a distinct article, and that the distribution of 

 Mr. Edwards, founded primarily upon the manduca- 



tory or suctorial nature of the mouth, appears to fi 

 to be less natural than that given below. 



CLASS CRUSTACEA. 



Section I.MALACOSTRACA. Shell of a solid consistence ; 

 legs ten or fourteen ; mouth with a labrum, two 

 mandibles, four maxillae, six or ten (according to 

 the number of legs) foot jaws. 



Sub-section 1. PODOPHTHALMA. Eyes on footstalks. 



Order 1. Decopoda. Legs ten; foot jaws ten; 



branchiae in a cavity at the sides of the thorax ; 



divisible into two sub-orders. 



Brachy ura (short tailed crabs See BRACK YURA). 



Macroura (lobsters, &c. See BRACHYURA and 



MACROUUA). 



Order 2. Stomapoda. Branchiae not inclosed be- 

 neath the shell at the sides of the thorax ; legs 

 more than ten. 



Sub-section 2. EDRIOPHTHALMA. Eyes not elevated 

 on footstalks. 



Order 3. Amphipoda. Body compressed; mandi- 

 bles palpigerous. See AMPHIPODA. 

 Order 4. Laewodipoda. Abdomen rudimental, with 

 only the rudiments of one or two pairs of 

 appendages. See CAPRELLA. 

 Order 5. Isopoda. Body depressed ; abdominal 

 appendages flat and plate like ; mandibles not 

 palpigerous. 



Section 2. ENTOMOSTRACA. Shell not solid; legs 

 variable in number ; mouth very variable. 

 Order 6. Branchiopoda. See this article and its 



divisions. 



Order 7. Pacilojioda. Mouth suctorial, or desti- 

 tute of mandibles and maxilhv, but defended 

 bv the ambulatory legs which perform this 

 office. Divisible into the sub-orders Xiphosura 

 (or king crabs), and the Siphoiwstoma (or fish 

 parasites). See CALIGIDES. 

 As these kinds of tabular sketches are best eluci- 

 dated bv references to figures, we will direct our 

 readers for an illustration of the Decapod Bnichyum 

 to Vol. 1. p. 722, for a figure of Carcinus mcc-nas; of 

 the Decapod Macroura, to p. 167 of this volume, for a 

 figure of the Cray-fall ; of the Amphipoda, to Vol. I. 

 p. 95, for a figure of Gammarus Pafi.v, by mistake 

 called Pernys, which is the Comphium iongicorne ; of 

 the L(Emorii/ioda, to Vol. I. p. 691, for a figure of 

 Caprella Phasma; of the Ixojjoda, to Vol. II. p. 25, 

 fig. 2, representing Armadillo vnlgaris ; of the Bran- 

 c/noj)oda, to Vol. I. p. 626, representing the Brine 

 Shrimp; and we here figure the Argulus foliaceus, 



* Zoological Illustrations; p. 9. 



1, the animal magnified ; 2, one of the large anterior sucking 

 feet; 3, the rostrum) 4, natural length. 



belonging to the order Pcecilopoda (sub-order Sipho- 

 nostoma}, an account of the habits of which will be 

 found under the article CALIGIDES. The remaining 

 classes Stomapoda and Xiphosura, will be illustrated 

 in subsequent articles. 



CRYPTANDRA (Smith). A genus of curious 

 shrubs from New Holland. Class and order Pen- 

 tandria Monogynia, and natural order Rhamncee. 



