128 K. BAMUNNl MENON. 



tery, howevei'j extends farther forwards, and reaches up to 



the wider anterior portion of the proboscis cavity. The 



mesentery is more muscuhir in its posterior part than in its 



anterior, which is practically a band of connective tissue. 



It may be doubted whether this portion can be really called 



a mesentery, but, there can be no doubt that the mesentery 



proper extends a considerable distance beyond the basal 



organs. This anterior extension of the mesentery is regarded 



— as far as I have been able to make out — as characteristic 



of the genera with a vermiform process, viz. Glandiceps and 



Schizocardium, and it is interesting to find it in Dolicho- 



glossus, in which no vermiform process has been detected. 



The tip of the proboscidial diverticuluni is bent dorsally, as 



in D. Kowalevski. The diverticulum is hollow, but the 



cavity of the anterior portion is extremely narrow. In 



median longitudinal sections the neck of the diverticulum is 



seen to be very long, and to open into the buccal cavity far 



behind in the collar region. This posterior position of the 



opening (fig. 3) may be partly due to a slight retraction of 



the proboscis into the collar during preservation. The 



central blood- sinus is very conspicuous, and is distended 



dorsally just behind the heart vesicle. The heart vesicle is 



remarkably small. In a series of longitudinal sections each 



about -^jy mm. thick, the heart vesicle covers only ten 



sections. Its other dimensions can be gathered from fig. o. 



Its posterior wall does not touch the wall of the proboscis. 



A similar reduction in the size of the heart is also mentioned 



in Stereobalanus (Balanoglossus) Canadensis. The 



body of the proboscis skeleton is long, and extends into the 



posterior region of the collar ; the chondroid tissue is very 



poorly developed. Its posterior limbs reach to the hind end of 



the collar. The proboscis pore is placed on the left side of the 



median line at the posterior end of the neck of the proboscis. 



Collar. — The collar has the usual structure. The dorsal 



mesentery is present throughout the whole extent of the 



collar, the ventral only in its posterior half. Transverse 



muscles arc present in the ventral wall of the periha3mal 



