172 



ANNELIDA. 



Fig. 76. 



is contained in the rest of the apparatus. 

 These organs (Jig. 74, g) are generally regarded 

 as accessory vesicles, and they vary both in 

 number and form in different species. 



The female apparatus is of much less mag- 

 nitude, but also presents a sufficiently com- 

 plicated structure : it is situated between the 

 two canals leading to the accessory vesicles of 

 the male apparatus, and is a little posterior to 

 the penis. The external orifice, of which we 

 have already spoken, communicates with a short 

 canal (jig. 74 and 76, //), of a greyish colour, 

 which leads to a sort of 

 pouch (i). This, accord- 

 ing to some authors, 

 is analogous to an ute- 

 rus, but in the opi- 

 nion of other natura- 

 lists is merely a copu- 

 lative vesicle for the pur- 

 pose of retaining the 

 fecundating liquid which 

 is there deposited by 

 the male in the act of 

 copulation. This sac is bent upon itself, and 

 a duct (j) may be observed to be continued 

 from the anterior extremity which leads to the 

 ovaries (k) : these are small whitish bodies two 

 in number, and in close approximation to one 

 another. 



In the earthworm, the only parts that can be 

 regarded as male organs are some sacs or 

 vesicles varying in number from two to seven, 

 and situated in a longitudinal series on either 

 side of the ventral aspect of the body towards 

 its anterior extremity. Each of these vesicles 

 adheres to the parietes of the splanchnic cavity, 

 by a small canal opening directly outwards by 

 pores placed on the posterior and inferior part 

 of the corresponding ring: there is farther a 

 canal of communication, which is continued 

 directly from one vesicle to another of the 

 same lateral series ; and at the season of co- 

 pulation there is found in the interior of these 

 organs a viscid liquid abounding with seminal 

 microscopic animalcules. The outlets of the 

 female apparatus occupy the sixteenth segment 

 of the body, and are continuous internally 

 with two narrow canals directed forwards, and 

 situated on the internal side of the above 

 mentioned vesicles. Having reached the ova- 

 ries, each of these canals (Jig- 77, ) divides 

 into two branches (6), 

 which bend inwards and 

 terminate by a globular 

 enlargement (c). This is 

 seen with the assistance of 

 the microscope to be itself 

 formed by a continuation 

 of the canal puckered up 

 into numerous folds, which 

 are enveloped in a com- 

 mon membrane. To each 

 of these enlargements are 

 appended a pair of ova- 

 ries, the entire number 

 of which is consequently eight, four on either 

 side. The colour of these ovaries is whitish, 

 their texture pulpy, and their interior is beset 



Fig. 77. 



with numerous minute vesicles, which are the 

 ova. At the period of copulation the ovaries 

 are filled with a whitish fluid, which is pro- 

 bably the spermatic secretion, but it is not 

 easy to comprehend how the male apparatus 

 can introduce it into that part.* According 

 to Redi, the ova, after being detached from the 

 oviduct, pass along the whole extent of the 

 body towards the vicinity of the anus, whence 

 they are expelled by two orifices stated to be 

 near the termination of the alimentary canal 

 or to open in its interior. According to Mon- 

 tegre it is the fetus and not the ovum which 

 traverses the body to escape by the above 

 passages, and the lumbrici according to this 

 view are viviparous. This statement has been 

 adopted by many authors without perhaps 

 sufficient examination; but, according to recent 

 observations by Duges, it would seem not to 

 be correct, and that what have been regarded 

 as the young of the earthworm are in fact a 

 species of intestinal worm. 



In the na'is the male organs are less nume- 

 rous than in the lumbrici, but differ very little 

 in other respects. They consist of a single 

 pair of vesicles opening externally by a wind- 

 ing canal, which terminates by a small fissure 

 on the eleventh segment of the body. The 

 ovaries are disposed in four principal masses, 

 between which there winds a long oviduct, 

 of which the extremity can be protruded out- 

 wardly like a penis.-j- 



In some annelida, as the clepsina carena, 

 the ova are developed and hatched before 

 exclusion, so that the young are born alive; 

 but most of the class are oviparous, and what 

 is very remarkable, the same ovum sometimes 

 incloses the germs of many embryos : this is 

 the case in the earthworm, each ovum of which 

 produces two individuals, and in the leech the 

 ova contain severally as many as eighteen 

 embryos. One might at first view suppose 

 that the same circumstances obtained in the 

 na'is; but what appears to be an ovum with 

 multiplied germs is in reality nothing more 

 than an aggregate of simple ova. 



Reproduction. Some annelida not only per- 

 petuate the race by the ordinary modes of gene- 

 ration, but enjoy the singular faculty of pro- 

 ducing new individuals by a transverse division 

 of the body. A na'is or an earthworm cut in 

 two and placed under favourable circum- 

 stances, will continue to live, and each moiety 

 will become, in appearance at least, a perfect 

 animal. This fact, which was first determined 

 by Reaumur and Bonnet, has since been veri- 

 fied by M. Duges, Sangiovanni, and many 

 other observers : the anterior portion of the 

 animal reproduces a new tail, and the posterior 

 portion developes a head. 



That faculty which the two portions of the 

 earthworm's body possess of manifesting the 



vital properties independently of one ano- 

 her, and even after having been separated, 



may be explained to a certain degree by 

 the known structure of these animals and 



* See Willis, Duges, &c. 

 f See Duges, op. cit. 



