AXNULATA. 225 



ORDER II. Suctoria. 



Body annulate, without setas, terminated by a prehensile cavity 

 posteriorly or at both extremities. External branchiae none. 



Family III. Hirudinea. (The characters of the order are also 

 ;hose of the single family.) 



The family of the blood-suckers (leeches) is formed from the genus 

 Hirudo L. These animals are able to convert the anterior extremity 

 of the body into a suctorial cavity, or have there, as at the posterior 

 extremity, a round suctorial disc. They creep along the ground, by 

 affixing this sucking apparatus and by alternately contracting and 

 extending the body. They swim with a serpentine and sinuous 

 bending of the body, which is effected with much velocity. 



Comp. on this family MOQUIN-TANDON, Monographic des Hirudintes, 

 nouv. edit, av.pl. color. Paris, 1846, 8vo. 



A. Head made up of several segments of the body, slightly or 

 not at all distinct from the rest of the body, capable of change into 

 a suctorial acetabulum by its own motions. 



Clepsine SAV. Body depressed. Mouth unarmed, furnished 

 with a proboscis exsertile, tubular. Eyes 2 6 (sometimes eight ?) . 



Sp. Clepsine hyalina, Hirudo hyalina L., TREMBLEY, Polyp. PI. vn. fig. 7 ; 

 Clepsine complanata, &c. 



This animal lays its eggs on water-plants (Stratiotes aloldes) and continues 

 to sit thereon. The eggs also attain their development even when the mother 

 is driven away, but are then frequently affected and spoilt by confervas. These 

 eggs are thin-skinned vesicles in which numerous yelk-spheres, 15 to 30, 

 are contained, and from which a corresponding number of young are 

 developed. 



Comp. on the species of this genus F. MUELLER, De Hirudinibus circa 

 Berolinum hucitsque observatis, Berolini, 1844, 8vo, and T. BUDGE, Clepsine 

 bioculata. Mit 2 Taf. Bonn, 1849. 



Under this genus F. MUELLER also places Hirudo marginata and Hir. 

 tessulata of O. F. MUELLER, though the last has eight eyes, whilst in 

 Clepsine the number does not exceed six ; the arrangement of the eyes is 

 in two rows longitudinally which meet forwards, just as in the six-eyed 

 Clepsines; the blood also is white. 



Nephelis SAV. Body elongate, posteriorly incrassated, obtuse, 

 with acetabulum obliquely terminal. Mouth unarmed. Eyes eight, 

 disposed in a series semicircular, transverse. 



VOL. I. 15 



