oOG ARTHROrODA 



Order I. Branchiopoda. 



The Branchiopoda are relativolv large wiih numerous segments, leaf-like 

 appendages, long, chambered heart, and lack swimming antenna\ \\ ith tew 

 exceptions thev are inhabitants of fresh water. Accon.iing to the development 

 of the carapace thev are subdivided into three families. 



I. .\P0DiD-i-:. Bodv depressed, with large oval undivided carapace. Eggs 

 carried in brood capsules formed by a pair of appendages. .1 /);/.?* (lig. 37(3), 

 LcpiJiinis* Frol.hwi.': of the Cambrian is apparently an .\podid. 2. Br.vn- 

 CHIPID.E. Bodv without carapace, the second antennci? of the male large and 

 modified for clasping the female. The female carries the summer eggs in a 

 wide 'uterus' in the abdomen. Prainhlpiis* (fig. jSj"), fresh water; Artoiiia* 

 in brine; one has been transformed into the other by clianging the water from 

 fresh to salt or the reverse. 3, Esthkriip.k. Body laterally compressed and 

 enclosed in a bixahe shell, com])ound eves fused; males verv rare. Esllnria,'^ 

 Limnadia,-'' fresh water. 



Order II. Cladocera. 



Like the esthcriids the small Cladocera have the bodv enclosed in a bivalve 

 carapace, which in sotne is small and reaches back only over the first trunk seg- 

 ments, in others is large, enclosing the body, with a notch for the protrusion of 

 the head, while behind it terminates in a sharp spine. The head bears a pair of 

 large swimming antenn;e and a much smaller first pair bearing olfactory bristles 

 and, in the male, hooks for clasping the female. The body consists of few seg- 

 ments, the heart is a simple sac, and the fused faceted eyes are capable of motion 

 in a special optic capsule. The young eggs in the sexual organs always occur 

 in groups of four (fig. 3S3). Of these but one grows into an e^gg, the others 

 serving this as nourishment. Larger eggs with more yolk occur when several 

 groups fuse to form a single egg. The summer eggs arise from a single group, 

 the winter eggs from several groups of primordial ova. The space between the 

 back of the animal and the shell serves as a brood pouch. The larger winter 

 eggs — one or two in number — frequently remain for a while in the brood 

 chamber and are there enveloped in a peculiar shell, the cphippiuiu. consisting 

 of two chitinous plates, like watch crystals, their edges closelv appressed. 



D.VPHXID.E. Shell well developed; DapJiiiia* (fig. 3S3"), l^osmiiu.'^ PoLY- 

 PHEMID.E. Shell small, only functioning as a brood case; head with an enor- 

 mous eye and large swimming antenna; no phyllopodous feet; marine and lacus- 

 trine. Lcptodora liyaliiuv' appears at night, sometimes in great numbers, in 

 some of our lakes. EvjJiic* (fig. 3S4), marine. 



Sub Class III. Copcpoda. 



A general description of the copcpods can oiily apply to the non- 

 parasitic forms, sii^ce many of tlic parasites arc so degenerate (ligs. 0, 38S) 

 as to be recognized even as arthropoils only by a knowlcHige of the develop- 

 ment. The si.xteen somites of the body are nearly equally divided among 

 the three regions— head (0), thorax (5), and abdomen (5)— of the aiumal. 

 (In Cyclops the first thoracic segment is fused with the liead, the first two 

 abdominal segments are fused— tig. 7.) The last abdominal segment 

 is two-forked, forming the Jural. While the abdomen lacks appendages, 

 the thorax bears typical biramous appendages, consisting of a two-jointed 



