238 ANNELIDA. 



(620.) The second generative annulus in the order mentioned is ex- 

 clusively ovarian, and it is not difficult to see that the mass and the 

 base of the ciliated tube run together, and become blended into one 

 structure. The most minute dissection fails to isolate the duct which, 

 it may be supposed, leads from the ovary ; but, as in the case of the testes 

 behind, it is certain that the gland and the tube must have a common 

 outlet. The ovary is considerably smaller than the testes ; its capsule 

 is more dense and vascular, and its interior structure is much more 

 copiously supplied with blood. 



(621.) In the common Earthworm the second, third, and fourth ge- 

 nerative segments are ovarian, each being anatomically only a repetition 

 of the other ; all are constructed upon the same plan. 



(622.) The fifth segment, from behind, is again testicular, exactly 

 resembling the first, so that the first and the last segments in this re- 

 gion are testicular, the three intermediate ones being ovarian. 



(623.) The ovaria of Lumbricus are much more transient in their 

 duration than the testes ; the latter, in a certain condition, are always 

 present at every season of the year, the former only in the summer 

 months. The ova, while yet in the ovaria, are beautifully clear trans- 

 parent cells. In August and September they seem to consist of nothing 

 but germinal vesicles ; afterwards appear the germinal spots, and then 

 the rudimentary vitellus. At a subsequent stage, just before their extru- 

 sion from the body, they become covered with a cocoon or characteristic 

 capsule, each capsule containing many ova. This capsule is a compound 

 of chalk and mucus. In the median line between the ovaria there are 

 situated two or more glandular bodies, the contents of which, under the 

 microscope, are found to consist of nothing but carbonate of lime 

 doubtless the source of the chalk. 



(624.) Both in the ovarian and testicular segments there are sacculi 

 attached to the bases of the segmental organs, which in the former 

 case serve as receptacles for the ova (vitellaria), and in the latter as 

 receptacles for the semen. In one case the ova acquire their calcareous 

 capsules; in the other the sperm-cells become developed into active 

 spermatozoa. 



(625.) The eggs, when laid, are said by Duges to be two or three 

 lines in length. In fig. 115, A, one of them, enclosing a mature em- 

 bryo, is delineated ; its top is seen to be closed by a peculiar valve-like 

 structure adapted to facilitate the escape of the worm, and opening 

 (fig. 115, B) to permit its egress. Another remarkable circumstance 

 observable in these eggs is that they very generally contain double 

 yelks, and consequently two germs ; so that a couple of young ones are 

 produced from each. 



(626.) It is very generally believed that the Earthworm may be 

 multiplied by mechanical section, the separated portions reproducing 

 such parts as are removed in the experiment, and again becoming perfect. 



