INVERTEBRATE ZOOLOGY. 107 



teriorly by a pair of processes, which project dorsally from the ab- 

 domen, and which may be drawn downward to allow the escape of 

 the young. The brood cavit)' is filled with a special flnid for the 

 nourishment of the young, which develop here without metamor- 

 phosis and escape in the same form as the adult, 

 (c) Eggs and ephipphuii. The eggs which develop parthenogenetically 

 are thin shelled, develop very rapidly and produce only females. 

 Such eggs are called ' ' summer " eggs. The fertilized or • • winter '' 

 eggs are hard-shelled and receive, when in the brood cavity, a second 

 covering, called the saddle or ephippiuiii. which is produced by the 

 shell. An ephippium contains in this species two eggs, and is depos- 

 ited in the mud, in which state the eggs can survive the winter, or 

 endure drying up. Winter eggs produce both sexes. 



Type XV.— Cypris sp? 



79. This is one of the most refractory objects of study, being too small 

 to dissect, too oj)aque to treat like the former two tyi)es, and covered with 

 thick chitinous shells, rendering it difficult to cut. It is best in a general 

 course to be content with a superficial examination. They may be first 

 studied alive, observing the movements of the shells, and of the appendages. 

 For special study of the latter, a large specimen may be selected and one lat- 

 eral shell lifted off with needles, or they may be opened by treatment with 

 hot Perenyi's fluid [72]. The shell is closed l\y a transverse adductor muscle, 

 which tmites the two valves at their centers. When this muscle is relaxed, 

 an elastic ligament, situated at the dorsal hinge, draws the shells apart. An 

 impression for the attachment of this muscle may be seen on the inner sur- 

 face of a clean, empty shell. There are only seven pairs of appendages, 

 borne on the anterior body portion, which corresponds to head and thorax; 

 the abdomen is attenuated and resembles the appendages. The appendages, 

 with their forms and uses, are as follows : 



Ant J ) Long, leg-like, used in locomotion. The second pair modified 



Ant^> S in male. 



Md Large — provided with a palpus, and flattened piece or fan-plate. 



Mxj With a j)alpus and flattened fan-plate. 



Mx._, With a small, two-jointed palpus, and rudimentary fan-plate. 



Legi This is often called the maxilliped. Used for locomotion. 



Lego ■■ Cleaning foot," curved backward and used in cleaning out the 

 shell. 



