520 CYCLOSTOMATA. 
tube (the cesophago-cutaneous duct) opens from the 
cesophagus to the exhalant aperture. Perhaps some water 
enters by it in inspiration. 
Vascular system.—The blood contains the usual ame- 
boid leucocytes and red blood corpuscles, elliptical in 
form (circular in the lamprey). It is collected from the 
body in anterior and posterior cardinals, passes through 
a sinus venosus into the auricle of the heart, thence to 
the ventricle, thence along a ventral aorta, which gives off 
vessels to the respiratory pouches. From these the purified 
blood passes dorsalwards in efferent branchial vessels, which 
unite posteriorly, to form the dorsal aorta, while from the 
most anterior a branch goes to the head. The portal vein 
has a contractile sinus which drives blood through the 
liver. The pericardium is in free communication with the 
general body cavity. es 
Excretory system.—The segmental pronephric ducts persist, 
and give off short lateral tubules, metamerically arranged, ending in 
globular malpighian capsules. The pronephros is functional in the 
young form, and at least part of it persists throughout life, e.g. in a 
lymphoid structure beside the pericardium. 
The ducts end by separate pores on a papilla within the integument- 
ary cloaca, 
Reproductive system.—//yxine is a protandrous herma- 
phrodite, spermatozoa being formed at an early period, 
and ova afterwards. The reproductive organ is simple, 
unpaired, and moored by a median dorsal fold of peri- 
toneum. Owing to the large size of the ova, the ovary is 
very conspicuous in full-grown forms. When the ova are 
freed from the ovary, they pass into the body cavity. Each 
has an oval horny membrane, with a circlet of knobbed 
processes at each end. By these they become entangled 
together. There are no genital ducts, but just above the 
anus there is a large genital pore opening from the body 
cavity into the integumentary cloaca. The development 
is still unknown. 
Besides Myxcne glutinosa, two other species are known—one from 
Japan, another from the Magellan Straits. The southern JZ, australis 
lives in shallow water close by the shore, but the others live in deep 
water. The genus Bdellostoma, from the Pacific coasts America, 
off the Cape of Good Hope, etc., is nearly allied. 
