Tl IK MALACOSTRACA. 



The Cirripedia are almost exclusively marine, only a few 

 species tolerating even brackish water, The Thoracica alone 

 have yet been found in the fossil state. The oldest knoun 

 genus, PollicipeS) occurs in the lower o6lite ; there is a single 

 cretaceous species of Verruca, but the sessile (impedes be- 

 come luminous only in the tertiary epoch. 



The RIIIZOCEPIIALA (PeltO(/<r*f> /, >'*/ v. ///////) are small and 

 parasitic; usually upon the abdomen of other (',- facea 

 (Podophthalmia). The body is like a sac or li>k, .-in. I <1. 

 of segmentation and of limbs. r Jhe aperture of the sac is 

 funnel-shaped, and supported by a ring of chitin. The circum- 

 ference of the funnel gives off a number of root-like processes, 

 which branch out through the body of the infested animal. 

 The alimentary canal is obsolete, and there are no cement - 

 glands. They are hermaphrodite, and the young, like those 

 of the other Pectostraca, pass through a Nauplius and a 

 Cypris stage. 1 



THE MALACOSTRACA. The groups of Crustacea known as 

 the Podophthalmia, the Cumacea, the Edriophthabnia, and 

 the Stomatopoda, are here included under this head. 



The body consists of twenty somites (counting that which 

 bears the eyes as one), and, of these, six (bearing the 

 antennules, antennae, mandibles, and two pairs of maxilla-) 

 constitute the heiul : eight enter into the thorax, and bear 

 the foot-jaws and ambulatory limbs; and six form the abdo- 

 men and swimming limbs. In some few instances the num- 

 ber of somites is reduced, but they never exce< d twenty. 



The .Y'//^//>/x-form of the free embryo is rare, but occurs 

 in some cases (Penevs). In others (My sis) it is represented 

 only by a temporary condition of the embryo, during which, 

 however, a chitinous cuticula is formed, and subsequently 

 shed ; and what appear to be remains of such a transitory 

 record of an original \<n/)>1!)ix state, are seen in trany Am- 

 j>h>}>()<1(t and I$o)><t<t, which nearly attain their adult form 

 within the egg. In most Podopkthalmia the embryo leaves 

 the egg not as a Nauplius, but as a Zomt, which lias thora- 

 cic, but no abdominal, appendages, and in many respect 

 sembles a Cop'epod. 



1 The term (ty/i/vs-staire. usually applied to that condition -of the larva? of 

 the F,'f,*f>'(i,''r in which they atv provided \vith :i bivalve carapace, must not 



n to inn 1 ;;l l affinity with the Odracoda. On the COT/ 



the 1 irvu in the Ctyprw-stage is much more similar to a Copepod or Brenchi- 

 opod. 



