ON THE BRITISH ANNELIDA. 253 



during the congress 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 can make not the slightest difference whether the ova are expelled as such, 

 or whether, owing to tijeir being retained by accidental circumstances until 

 they are hatched internally, the young leeches make their appearance in a 

 living state*." 



What is described in the preceding passage is rightly described. There is 

 in nature what it purports to define — a median pear-shaped sacculus, from 

 the fundus of which a small coiled caecal process depends. But is it possi- 

 ble, on any physiological principle, that this simple sacculus can be the femi- 

 nine correlate of that complex, elaborate and highly-developed testicular 

 apparatus previously described in the same animal ? Is it not a priori impro- 

 bable that one moiety of the reproductive system should coincide to the An- 

 nelidan type, namely, that of exhibiting a tendency to segmental repetition in 

 a longitudinal series, — while the other, and unquestionably the more important 

 half, should be concentrated into the narrow limits of a solitary sacculus ap- 

 pended only to one ring of the body ? The median sacculus originally disco- 

 vered by M. Duges does exist, but is constituted, as will afterwards be shown, 

 the least important constituent of the generative system. Desirous to assign to 

 M. Duges the credit to which he is really entitled, it is now proposed to quote 

 the description given by this anatomist of those organs in the Leech which 

 he was the first to discover, and which he, and, after him, all subsequent com- 

 parative anatomists have designated '■'■the respiratory sacculi." It will be 

 seen that his descriptive statement, with reference to these "respiratory sac- 

 culi," agrees in its leading points with the anatomical account which the 

 author will afterwards have to present of the true and indisputable feminine 

 element of the reproductive system of the Leech. 



" It has already been mentioned, that in the Abranchiate Annelidans, the 

 organs provided for respiration are a series of membranous pouches, commu- 

 nicating externally by narrow ducts or spiracles, as they might be termed, into 

 which aerated water is freely admitted. These respiratory sacculi in the Leech 

 are about thirty-four in number, seventeen being visible on each side of the 

 body ; they are extremely vascular; and in connection with every one of them 

 there is a long glandular-looking appendage, which was looked upon until 

 lately as being intended to furnish some important secretion, but which re- 

 cent discoveries have shown to be connected with the propulsion of the blood 

 over the walls of the breathing vesicle." " On examining minutely one of 

 the respiratory pouches, its membranous walls will be seen to be covered with 

 very fine vascular ramifications, derived from two sources : the latero-abdo- 

 minal vessel gives off a branch, which is distributed upon the respiratory 

 sacculus; and there is another very flexuous vsscular loop, derived from the 

 lateral vessel itself, which terminates by ramifying upon the vesicle in a 

 similar manner. The walls of the loop are extremely thick and highly irri- 

 table ; but on tearing across, the internal cavity or canal by which it is per- 

 forated, is seen to be of comparatively small diameter, so that we are not sur- 

 prised that, although such appendages to the respiratory sacs were detected 

 and well delineated by Delle Chiaje and Moquin-Tandon, their nature was 

 unknown, and they were supposed to be glandular bodies appropriated to 

 some undiscovered use. From the arrangement above described, it is evident 

 that small circular currents of blood exist, which are independent, to a certain 

 * Qp. «7. p. 201. 



