262 REPORT — 1851. 



side of the median line, and open externally by orifices (fig. 69), seen outside 

 on the abdominal surface. They are simple csecal vesicles, communicating 

 ■with no detectable duct. It is not improbable, from the analogy of the in- 

 tromittent organs, which will be subsequently shown to be contained within 

 vesicles of a similar character in Nais, that they may lodge an intromittent 

 instrument of some sort, though its presence has not yet been proved by actual 

 observations. It is only on the supposition that some such organ is con- 

 tained witliin these pouches that their mechanical functions can be under- 

 stood. We are now prepared to enter upon a minuter description of the 

 ntero-ovarian organs. These marvellous organs are constructed in the 

 Earth-worm with great exactitude on the model of those of the Leech. A 

 tube (a, fig. 68) proceeding from the common testicular duct (b, b, fig. 66) 

 runs along the upper part of the segmental dissepiment, which serves, as al- 

 ready explained, to convey the sperm-fluid into the uterine cavity. This tube 

 is embraced, as at a', a" (fig. 68), by stromatous tissue, which is densely 

 charged with ova. These ova seem successively to be thrown into the channel 

 of duct a, (fig. 68) where they are brought under the direct agency of the 

 fertilizing fluid ; thus fecundated they travel onwards in the line of the cir- 

 cumference of the ovarian uterus, b, b', b", b'", undergoing greater and greater 

 development, until finally in the passaged, terminating in the outlet rf', they 

 dehisce, and the young appear alive and active. After a sojourn of variable 

 duration in this passage, the young escape externally through the outlet d', D. 

 To the concavity of this organ a pouch or marsupium is appended. This 

 part, during the breeding season, is crowded with ova on the point of giving 

 escape to the young, c'. From this marsupium the ova descend as at b'", 

 in a very advanced state of development. It may be designated the true 

 uterine segment of the utero-ovarian organ, the place wherein the ova un- 

 dergo the process of incubation, that in which the young are hatched. The 

 whole of the interior (except the marsupium) of the ovario-uterine passages 

 are lined with vibratile epithelium. The cilia are active and vigorous during 

 the season of reproduction, but undistinguishable during the rest of the year. 

 A comparison of this organ with that of the Leech will show that the so- 

 called " respiratory sacculus" (Duges) of the Leech is altogether absent in 

 the Earth-worm. Considering the difference in the disposition of the male 

 organs in the two species, the absence of this singular appendage in Lum- 

 bricus can excite no surprise. With this exception the reproductive systems 

 of these two worms are formed on one and the same principle. 



During the reproductive season, in the Earth-worm it is a matter of easy 

 observation to trace the evolution of the ova throughout all its phases. It 

 appears first (1, fig. 70) under the character of a minute, pellucid, nucleated, 

 orbicular cell, of which the germinal vesicle and its contained germinal spot 

 exceed very slightly in transparency the surrounding vitelline mass. The 

 first appreciable departure from this unimpregnated type, which occurs in 

 consequence of fertilization, consists in a thickening of the vitellus (2), by 

 which, by contrast, the germinal vesicle is rendered much more distinct, the 

 germinal spot at this stage being only obscurely perceptible. 



Under the succeeding phase (3) the germinal spot presents itself under 

 the character of a double-cell, surrounded by a pellucid zone, which is evi- 

 dently still the germinal vesicle. At the next stage (4) the double-cell has 

 multiplied into a series, arranged linearly and slightly curved to conform to 

 the circumference of the vitelline membrane. This line of cells is still sepa- 

 rated from the material of the yolk by a very transparent interval, definedly 

 bounded, evidently by a membrane. This membrane must be the involu- 

 crum of the germinal vesicle. 



