MUSEUM OF COMPARATIVE ZOOLOGY. 207 



River group at Cincinnati, Ohio.* The former compares with the leg 

 as found in Ceraurus and the latter with the leg as restored in 

 Cahjmene. 



Uranchial Appendages. — The branchire have required more time 

 and labor to determine their true structure than any of the appendages 

 yet discovered. They were first regarded as small tubes arranged 

 side by side, like the teeth in a rake ; then as setiferous appendages, 

 and finally as elongate ribbon-like spirals and bands attached to the 

 side of the thoracic cavity, the epipodite being a so-called branchial 

 arm. All of these parts are now known to belong to the respiratory 

 system, but from their somewhat complex structure, and the various 

 curious forms assumed by the parts when broken up and distorted, 

 it was a long time before their relations were determined. 



The respiratory system is formed of two series of appendages, as 

 found beneath the thorax. The first is a series of branchiae attached to 

 the basal joints of the legs, and the second, the branchial arms, or 

 epipodites. 



The branchiae, as found in Cahjmene, Ceraurus, and Acidaspis, 

 have three forms. In the first they bifurcate a short distance from the 

 attachment to the basal joint of the leg, and extend outward and down- 

 ward as two simple, slender tubes, or ribbon-like filaments. In the 

 second form they bifurcate in the same manner, but the two branches 

 are spirals. These two forms occur in the same individual, but, as 

 a rule, the more simple ribbon-like branchia is found in the smaller or 

 younger specimens, and the spiral form in the adult. The exceptions 

 to this, however, are such that it has little value for any comparison of 

 structural features between the young and the adult. The first type of 

 branchia is shown by Fig. 5, Plate I., Figs. 2 and 3, Plate II., and the 

 second, by Figs. 4 - 10, Plate III. The latter are very interesting, 

 and a number of illustrations are given. The spiral structure is finely 

 shown by Fig. 5, Plate III., where, by the spiral being flattened, the 

 plane of the section has passed through it so as to show the tube 

 or ribbon as continuous and entire. Any of the sections. Figs. 4-10, 

 clearly prove that spirals were cut across, although there is no con- 

 nection between the segments except in Fig. 5. The bifid branchia 

 is illustrated by Figs. 9 and 10, Plate III. The branchia on the left 

 side of Fig. 3, and those of Fig. 8, Plate III., are formed of a finer, 

 more slender tube or ribbon, and coiled in a larger spiral. The 



* Received from Mr. S. A. Miller and Dr. C. A. Miller, of Cincinnati, Ohio. 



