GENERATIVE APPARATUS OP THE LEECH. 227 



with each other. There is no doubt that the seminal liquor is deposited 

 in this reservoir during the copulation of two individuals ; neither would 

 any one dispute that the ova are collected in the same cavity before they 

 are expelled from the body. As to the discussion whether the young are 

 born "alive or not, or, as it is generally expressed, whether leeches are 

 oviparous or viviparous, it is in this case merely a question of words ; for, 

 in a physiological point of view, it cannot make the slightest difference 

 whether the ova are expelled as such, or whether, owing to their being 

 retained by accidental circumstances until they are hatched internally, 

 the young leeches make their appearance in a living state. 



(591.) Leeches are oviparous. The ova remain in the uterus for some 

 time, where they become invested, first with a serous membrane, and 

 then with a glutinous fluid which remains attached to them after their 

 expulsion, and serves as a protecting covering after they are deposited in 

 the clay and holes of the sides of ponds. They generally deposit these 

 cocoons from May to the end of September. 



Such was the generally received view of the arrangement of the 

 generative organs of these Annelidans, as given in the first edition of 

 this work. We will now proceed to describe the reproductive system 

 of the Leech, as deciphered by Dr. Williams in his most recently pub- 

 lished version* : 



(592.) The segmental organs of the Leech tribe exist under very 

 readily demonstrated conditions. After pinning the common leech down 

 carefully to the trough, and opening the body by a longitudinal incision 

 along the dorsal aspect, the whole stomach and its diverticula must be 

 minutely picked away. The dissection should then be washed with very 

 gentle streams of fresh cold water, in order to remove the blood, which 

 obscures everything. The object being thus carefully cleansed, and then 

 floated in water, a full view of the segmental ovarian and the median 

 testicular systems will present itself. 



(593.) The one consists of a bilateral series of extremely delicate, 

 floating, pearly-looking membranous organs, equalling in the number of 

 their pairs that of the annuli marked upon the integument. The other, 

 more medianly situated and bilateral, also consists of two series (one on 

 either side) of little spherical white bodies, tied together by an interme- 

 diate thread, which unite at a common point anteriorly. A third element 

 should be noticed, namely the small sacculus, which, immediately behind 

 the anterior mass* of the united testes, lies also on the median line. 



(594.) According to Dr. Williams, every segmentary organ in the body 

 of the Leech is not only an excretionary instrument for the discharge of 

 the cavitary fluid, but is also an ovary. The tube which proceeds from 

 one limb of the organ and terminates in a spherical membranous vesicle 

 is the counterpart of the ciliated extremity of the segmental organs of 

 Nais and Lumbricus. Both open into the cavity of the body. In the 

 * Phil. Trans. 1858. 



Q2 



