AFFINITIES OF ECHIUEUS UNICINCTIJS. 87 



is very delicate, consisting of an epithelium of flattened cells {rp.), through which run 

 interlacing muscle-fibres {f.m.), forming an irregular network. The nuclei of these cells 

 are large and conspicuous, while the cell boundaries are quite distinct, though Spengel 

 says in Eckiurus Falhisii they are usually indiscernible. He also denies the existence of 

 a special system of blood-vessels which, according to Greeff, rim in the vesicle-wall — 

 in my preparations I see nothing to suggest that such a system of canals is present. 

 Greeff also says : " die Innenflache der Analkiemen ist mit wimpernden Cilien besetzt " ; 

 this is certaiuly not true of Echiunts imicinctus. 



Standing out from the vesicle-wall are many ciliated funnels (PL 10. fig. 35, /.), 

 on the structure of which I have nothing new to add. 



The vesicles are held in position by fine muscular fibres which attach them at various 

 points to the body-wall, but apart from this they float freely in the body-cavity beyond 

 their pomt of union with the rectum. I'l. 10. fig. 36 shows a transverse section of the 

 body at a point where the vesicles open — ventro-laterally — into the rectum, each through 

 a strikingly small aperture {a^, a'^) ; but according to some authors it is doubtful if this 

 should be looked upon as being a true part of the alimentary canal, or if it is not rather 

 an invaginated portion of the epidermis. There is, beneath the anal epithelium in this 

 region, a belt of peculiar tissue wiiich, in this species, extends forwards beyond the 

 openings of the anal vesicles; it has been thought to be modified glandular tissue 

 belonging to the epidermis, in which case the vesicles in Ee/ii/inis Kuic/i/cfiis would open 

 on the external surface which has become? secondarily internal. This special tissue has 

 been described by Spengel as " glandular " ; in all my preparations, however, it appears 

 to be a highly vacuolated connective tissue, differing from the ordinary connective tissue 

 only in possessing fewer fibrous elements and fewer nuclei (PL 10. fig. 37, t.p. ; La.) ; the 

 striking feature connected with this tissue is the abruptness with which it passes over 

 into the typical connective tissue {(m.), as is seen in fig. 37, where both types occur side 

 by side in one fold of the rectum-wall. The epithelium covering these different tissues 

 is the same, possessing, in both cases, an abundant supply of unicellular glands, whose 

 nuclei are situated at the basal ends of the cells ; many of these gland-cells sink down 

 into the tissue beneath, where they are seen cut across in all positions. Apart from 

 these glandular elements belonging to the epithelium, this special tissue gives no evidence 

 in support of the view that it is " glandular." What is its real significance is a 

 physiological problem which must he worked out on fresh or living material before it can 

 be settled satisfactorily. It is, however, probable that this animal performs some kind of 

 anal respiration, and that this area of vacuolated tissue is connected with the intake 

 of fresh sea-water, l)ecoming alternately turgid and flaccid. The significantly large 

 supply of radiating muscles on the rectum near the anus also suggests a suction action, 

 such as takes place in the rectum of a Holothurian, where there occurs a similar series 

 of muscles. In the straight posterior or rectal portion of the alimentary canal of 

 Echiurus unicinctiis (PL 7. fig. 5, r.) one finds two parasites — Trichodina and a Copepod, 

 and of these I hope later on to write a separate account. In all probability they 

 enter " per anum," for had they, or their eggs or spores, been taken in orally, they 

 would undoubtedly have been digested before reaching that part of the alimentary canal 



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