102 INVERTEBRATE ZOOLOGY. 



oars. Hence their motion consists of short rapid jerks. There are 

 many common species of this group ; Branchiopoda, Sub-order Cla- 

 docera, any one of which may be taken as a type. The form de- 

 scribed below is Simocephalus, a common form, larger than the av- 

 erage, and should be secured if possible. 

 3. Perfectly oval forms, entirely covered by large lateral shells, which 

 incltide the head. These are the smallest of all and seek the bottom 

 and sides of the glass, progressing by a steady, rolling motion, 

 caused by the projection of minute legs from between the edges of 

 the shells. They are Ostracods, mostly belonging to the genus Cy- 

 pris, which is taken as Type XV. The large species, variegated with 

 green and white, should be taken, if possible. 

 The methods of investigation are similar in all three types. The two first 

 are best studied alive, as they are so nearly transparent that the internal 

 organs are readily seen. Examination in a watch-crystal imder the dissecting 

 lens will give the general l)ody form, the use of the ai)pendages, mode of mo- 

 tion, etc., while they may be placed imder the compound microscope by iising 

 slide and cover. They may be quieted by chloroform, which may be applied 

 in drops, or by holding near them a bit of blotting paper, saturated with it. 

 Warm Perenyi's fluid poured over a groiip of Cypris, placed in a watch-crystal 

 will caiTse them to die with the shells beautifiilly expanded. They may be 

 preserved and sectioned as in 69. A mass of them may be handled at once by 

 filtering the water containing them through a bit of muslin, after which they 

 should be tied up in the muslin by a thread, and the liag and all subjected to 

 the action of the different reagents. They must be removed from the bag to 

 be placed in the paraiiftne oven and may be imbedded by poiiring the paraffine 

 containing them into a watch-crystal previously smeared with glycerine. The 

 position of the separate individuals may be seen through the translucent mass 

 and individuals that lie in a favorable position may be cut out in a cubic or 

 oblong piece, which may then be melted upon the end of a large block and 

 cut in the usual way. They are rather difficult to stain in toto. Slide stain- 

 ing gives good results. 



Type XIII.— Cyclops sp? 



73. External anatomy. The l)ody is covered dorsally by a carapace 

 which includes the head (five somites) and one leg-bearing thoracic somite. 

 Then follow four free thoracic somites, each bearing a pair of legs. The long- 

 tapering abdomen consists of five somites (first two fused in female) and ends 



