BRIEF REVIEW OF THE SYSTEM OF LIFE. 421 



Macrurans, — from the Greek for long-tailed^ the abdomen being rarely shorter than 

 the rest of the body. 



Among the Tetradecapods^ Figs. 378, 380 represent species of the tribe of Isopods (a 

 word meaning equal-footed), and Fig. 379 of that of Amphipods (feet of 2 kinds). Fig. 

 378 is the Sow-bug, common under stones and dead logs in moist places. Fig. 379 is the 

 Sand-flea, abundant among the seaweed thrown up on a coast. 



Under Entomostracans, the Cyclops group (Copepods) includes very small species 

 having a shrimp-like, or Caridoid, form, as in Fig. 381. Sometimes the male and female 

 differ much in form : 382 is male, and 381 female of Sapphirina Iris ; ab is the cephalotho- 

 rax, and bd the abdomen. In the Cypris group, the animal is contained in a bivalve shell, 

 as in Fig. 384, and they are hence called Ostracoids. 



In the Phyllopod group, the form is either Caridoid, approaching Cyclops, or like 

 Daphnia or Cypris; but the abdominal appendages or legs are usually foliaceous and 

 excessively numerous : the name is from the Greek for leaf-like feet. The Ostracoid Phyl- 

 lopods are multiplicate species (that is, excessive in number of body segments or limbs) of 

 the tribe of Ostracoids, and the Caridoid kinds often resemble multiplicate species of 

 Copepods. 



In the Cirriped or Barnacle group, the animal has usually a hard, calcareous shell, and 

 is permanently attached to some support, as in the Anatifa (Fig. 385) and Barnacle. The 

 animal opens a valve at the top of the shell, and throws out its several pairs of jointed 

 feet looking a little like a curl, and thus takes its food, — whence the name, from the 

 Latin cirrus, a curl, and pes, foot. The Anatifa has a fleshy stem, while the ordinary 

 Barnacle is fixed firmly by the shell to its support. Barnacles are common on the rocks of 

 the seacoast between high and low tide. The young Cirriped or Barnacle is a free-swim- 

 ming Ostracoid, much like Fig. 384 in form, but, on passing to the adult stage, it drops its 

 bivalve shell, and commences the sedentary life of the species, and the hard, permanent, 

 calcareous shell of the animal is then formed. As with other Crustaceans the animal 

 periodically casts its skin with progress in size, but not the hard calcareous shell about 

 the body. The shell of ordinary Crustaceans is not calcareous, but chitinous, and more or 

 less flexible ; the Cirripeds are an exception as regards this outer shell, but not in the 

 integument over the legs and body within this shell. The composition of the chitinous 

 covering of a lobster is given on page 73. 



Trilobites are Paleozoic Crustaceans related to the Isopods. They have the general 

 form of an Isopod, the higher division of the Tetradecapods, and were placed near this 

 group, with a query, by the author in 1852. But they are 

 Phyllopod-like or multiplicate species, with the exception of a -^86. 



few of embryonic relations. Like the Isopods, and unlike spe- x^^^^^^^^^ 



cies of Apus, and most other Entomostracans, they undergo no ^ /viv o JL^^ 

 metamorphosis. Trilobites are represented in Figs. 383, 386, // ^H^\^3 ^^Ss \\ 

 and 387-391. //^;^JP|5--^€lU 



In the Trilobite, the shell of the head-portion (ab. Fig. 383) 



is called the buckler; the tail (or properly, abdominal) shield, 



when there is one (Fig. 383, d), the pygidium. The buckler 



(a6) is divided by a longitudinal depression into the cheeks or 



lateral areas, and the glabella or middle area (Figs. 383, 386). '^^^^^^^Hf^d^^^^ 



The cheeks are usually divided by a suture extending from ,^ , • tt 



■^ '' " Dalruanites Hauemanni. 



the front margin by the inner side of the eye to either the 



posterior or the lateral margin of the shell. In Fig. 383 (Calymene Blumenbachii), this 

 suture terminates near the posterior outer angle. The glabella may have a plane sur- 

 face, or be more or less deeply transversely furrowed (Fig. 383), and usually has only three 

 pairs of furrows. The suture running from the anterior side of the eye forward or out- 

 ward, and from the posterior side of the eye outward (s in Fig. 386), is the facial suture; 

 a prominent piece on the under surface of the head, covering the mouth, is called the 



