ON THE BRITISH ANNELIDA. 257 



individual is inserted terminates In a convoluted ccecal tubulus. Between 

 this median organ and the great bilateral series of ovario-uterine organs there ' 

 is no communication Avhatever. If therefore during the union of two indi- 

 viduals a fluid is emitted by the male organ (k) into the interior of the sac- 

 culus (/), it requires no further argument to show that it can proceed no 

 further, that it can reach no other part of the reproductive system. In con- 

 gress therefore these two parts can subserve no other than the purposes of 

 first mechanically uniting the individuals, and secondly of stimulating the 

 sexual organs. During those periods when the fertilizing fluid is not required 

 for the oflfice of fecundation, it is probably discharged externally as a super- 

 fluous excretion in part through the intromittent organ (k). According to 

 this explanation, to the larger testicular bodies (h, h andy) should be assigned 

 the mechanical uses only of seminal receptacles, compressing what they may- 

 contain, either backwards into the ovario-uterine organs, or forwards to be 

 expelled through the penis as an excretion. The penis therefore is the only- 

 means common to the whole male system by which it communicates with the 

 exterior, the so-called " respiratory sacculi," as subsequently to be explained, 

 being the means by which each testis separately communicates with the ex- 

 terior. 



The sperm-cells of the Leech are represented at C (fig. 65) in their several 

 phases of evolution. 



It is here essential to add that the ova are first produced in a stromatous 

 layer which constitutes one of the coats of the ovarian uterus (B), and that a 

 large number of them are contained in a common capsule (B, p) until they 

 attain a certain degree of development, after which they may be recognised 

 near the outlet of the oviduct in a single and free state. 



Ova are never found in the so-called " respiratory sacculus " (B, o, e, e, e), 

 but, on the contrary and invariably, a small quantity o^ sperm-fluid : each of 

 these sacs is perforated (as at r, B) at the point where it is attached to the 

 integument by an orifice which opens directly externally. This vesicle, which 

 from the date of the writings of M. Duges has been rapturously described as 

 the " respiratory sac " of the Leech, correctly interpreted, is a true vesicula 

 seminalis. It is designed to receive the superfluous portion of the sperm 

 secretion as it passes from the testis to the ovarian uterus. Through the orifice 

 (r, B) this unrequired portion is discharged externally. Spermatozoa can 

 always be discovered in the interior of these vesicles. 



Their parietes are very scantily supplied with blood-vessels! What then 

 becomes of the blood so profusely poured over these parts by the contractile 

 thick-walled vessels of Duges? 



On the authority of Mr. Brightwell of Norwich, it is generally held that the 

 leeches are oviparous. His description bears the stamp of circumstantial 

 accuracy and truth, and tends to confirm the inferences which the author of 

 this Report has ventured to draw from anatomical investigations. 



Mr. Brightwell relates that "early in March of the present year (1841) 

 about seventy specimens of a small leech were taken from the back fin of a 

 roach caught in the river Wensum. They were the Hcemocharis piscium 

 and H. geometra of authors. These leeches being placed by themselves in a 

 glass vessel, and having fresh water put to them every morning, several in- 

 stances of sexual connexion were observed to take place immediately after 

 the fresh water was added, one of the leeches suddenly twisting itself round 

 the neck of another, and closing upon a longitudinal opening which at this 

 time was very conspicuous in the neck of each. During this union a white 

 substance could be perceived on the side of the part where the bodies were 

 connected. They continued united generally several hours, and in one case 

 1851. s 



