260 ANNELIDA. 



simple tube it sets out from this cavity. In the fundiis the current 

 leads up on one side, and down towards the outgoing limb on the 

 other. The two limbs by which the organ is tied to the walls of the 

 perigastric chamber are not similarly formed. The ingoing limb ex- 

 hibits a more glandular character, and its walls are considerably thicker 

 and more richly supplied with blood, than the other. About the middle 

 of its course it enlarges into a round gland-like body, the axis of which 

 is perforated by the tube. The ingoing limb commences in an ex- 

 ternal orifice on the abdominal surface of the animal ; so that the in- 

 going current which it serves to convey can only consist of sea-water, 

 which being thus introduced into the cavity, is driven out again, in 

 whole or in great part, by outwardly-acting cilia through the limb, 

 which also opens externally : none penetrates into the cavity of the 

 body. Nevertheless Dr. "Williams has no doubt, although he has never 

 been able to demonstrate the fact, that the outgoing leg of the looped 

 organ not only communicates directly with the exterior, but also, by a 

 lateral process, opens into the cavity of the body ; and by means of this 

 last process, the ova in the female and the sperm-cells in the male reach 

 the perigastric chamber. The ova in the female and the sperm- cells in 

 the male are abundantly found in the fluid of the general cavity ; and 

 the ova may also be actually seen in large crowds in the outgoing limb. 

 The ova at this point consist of clear, pellucid germinal vesicles : the 

 vitellus has not yet appeared ; after they have sojourned for some 

 time in the general cavity, the latter begins to show itself. According 

 to Dr. Williams, then, the segmental organ is the true ovary in the 

 female and the true testis in the male. The ingoing limb of the organ 

 is a highly glandular structure : its vessels are densely packed and spe- 

 cially arranged ; its walls are thick and stromatous ; and at its mid-point 

 is a notable glandular development. From the vascular system of this 

 gland proceeds the great vascular organ. 



(671.) To the one side of this great vascular system there are ap- 

 pended peculiar ca3cal pouches, from the other a dense capillary plexus. 

 This vascular appendage is the morphological equivalent of the blood- 

 system connected with the ovogenetic limb of the segmental organ of 

 the Leech, and of the botryoidal apparatus of vessels connected with 

 the segmental organ of Lumbricus, and must either be the receptacle of 

 an extra supply of blood to an organ susceptible of periodical expansion, 

 or it excretes something from the blood-proper into the cavity of the 

 segmental organ which is essential to the further development of the 

 generative products. It is quite certain that the ova and sperm-cells 

 pass through the last stage of their development in the perigastric 

 chamber. How they escape out of this chamber has never yet been 

 proved. 



(672.) Rathke and Grube have argued that Arenicola is androgynous. 

 De Quatrefages, however, from his knowledge of the development of the 



