ANNELIDA. 207 



aerated water thus taken into the system, and brought immediately 

 in contact with the deep-seated vascular net-work dispersed over 

 the intestinal parietes, must therefore necessarily contribute to the 

 respiratory function. Nevertheless, in addition to all this, we find 

 in every segment of the body a pair of membranous vesicles {fig. 

 82, v) communicating externally by lateral orifices, apparently 

 analogous to the respiratory vesicles of the leech ; and, in fact, by 

 many authors they have been described as constituting the breath- 

 ing apparatus.* Their real office, however, is but imperfectly 

 understood ; they evidently have not the same relation with the 

 circulatory system, which the lateral sacculi of the leech have been 

 found to exhibit ; are they then merely secreting follicles destined 

 to furnish a mucosity for lubricating the external surface of the 

 body, or are they aquiferous tubes adapted to introduce water into 

 the interior ? Future observations must determine these ques- 

 tions. 



(249.) Few points connected with the history of the earthworm 

 have given rise to so much speculation as the manner of their repro- 

 duction. The generative organs have long been known to be lodged 

 in the anterior part of the body, their position being indicated 

 externally by a considerable enlargement or swelling which extends 

 from the seventh to about the fourteenth segment, counting from 

 that in which the mouth is situated. On opening this portion of 

 the animal, a variable number of white masses are found attached 

 to the sides of the crop and gizzard (fig. 82, A, ^, A), which have 

 long, by general consent, been looked upon as forming the repro- 

 ductive system ; some having been regarded as representing the 

 testes, others the ovaria : yet so delicate are the connections 

 which unite these glandular masses, and such the difficulty of 

 tracing the ducts whereby they communicate with the exterior 

 of the body, that the functions to which they are individu- 

 ally appropriated have given rise to much discussion. The 

 Lumbrici have been generally acknowledged to be hermaphrodite, 

 that is, possessed of organs adapted both to the formation and 

 fertilization of ova ; and it is likewise well understood that the 

 congress of two individuals is essential to the fecundity of both, 

 as, in the earlier summer months, the mode in which they copulate 

 is a matter of constant observation. At such times two of these 

 animals are found to come partially out of the ground from 

 contiguous holes, and, applying together those segments of their 



* Sir E. Home. Lectures on Comp. Anat. 4 vols. 4to. 1323. 



