650 FRESH-WATER BIOLOGY 



Reproduction takes place in the spring and summer, some species 

 continuing to produce batches of eggs for five or six months. In 

 the Rhynchobdellae and HerpobdelJidae copulation consists in the 

 implanting by one individual of a horny, usually two-chambered 

 spermatophore on the skin of another. From this the spermatozoa 

 issue in a stream and, by a process that Professor Whitman has 

 aptly termed hypodermic injection, penetrate the tissues to the 

 ovarian sac where impregnation occurs. Among the Hirudinidae 

 a more definite act of copulation and reciprocal fertilization takes 

 place during which the filamentous penis of one individual 

 deposits a spermatophore within the vagina or at the genital 

 orifice of the other. 



The Glossiphonidae carry their eggs in several membranous 

 capsules attached to the venter, maintaining an undulatory move- 

 ment for their aeration. The young also remain for a time fixed 

 by a sort of byssus thread and later by the sucker, and are said to 

 be partly nourished by an albuminous secretion of the parent. All 

 other leeches form chitinoid cocoons or egg capsules from the secre- 

 tion of the deeper glands of the clitellum which hardens on exposure 

 to the water. The Ichthyobdellidae deposit a single ovum in a 

 small stalked capsule, the Herpobdellidae and Hirudinidae several 

 in an albuminous mass within a larger capsule, which in the case 

 of the former is a flat pouch attached by one side and in the 

 latter an ellipsoidal case with a thick, spongy, vesicular wall buried 

 in wet earth. 



Leeches have rather dull senses which arise in three sets of 

 cutaneous organs. Numerous goblet cells located in the lips are 

 taste organs and guide the leech on the trail of its prey. Tactile 

 organs are scattered all over the skin but are especially numerous 

 on the lips. Wave movements and light stimuli appear to affect 

 all parts of the body. The eyes are strongly sensitive and the 

 sensillae much less so to changes in the intensity of light. 



Leeches may readily be found by searching in the situations indi- 

 cated above. Sanguivorous species are easily collected by stirring 

 the mud in their haunts with one's bare feet and removing them 

 from the skin as they become attached, or by attracting them with 

 fresh blood placed in the water. They may be kept and studied 



