CHAPTEE IX 



ENTEROPNEUSTAi 



Bilaterally symmetrical, long, vermiform animals with soft skin. 

 The body is divided into (1) a preoral proboscis, (2) a short "collar," 

 (3) a long trunk. The wide mouth lies at the boundary between the 

 proboscis and the collar. The anus is terminal. The long intestine 

 may be divided into four sections. The mouth leads direct into (1) 

 the buccal cavity, which runs through the collar, and sends off a 

 diverticulum anteriorly into the i^roboscis. The buccal cavity leads 

 into (2) a branchial intestine, which is in open communication with 

 the exterior through numerous pairs of consecutive gill-pouches. The 

 branchial intestine passes, through an intermediate portion, into (3) 

 the hejiatic intestine, which is often provided with two longitudinal 

 rows of c?eca. Lastly, the hepatic intestine runs into (4) an efferent 

 intestine, which opens outwards through the anus. 



There is an unpaired proboscidal coelom, which opens outward at 

 the base of the proboscis either by a single pore on the left side, or by 

 two symmetrical pores. The coelom of the collar is paired, and there 

 are two pores at its posterior end. The crelom of the trunk is also 

 IDaired. The integumental and intestinal musculature are derived 

 from the coelomic walls. The nervous system consists of a layer of 

 nerve fibres in the integument, this layer being thickened to form a 

 mediodorsal nerve cord provided with ganglion cells, and a similar 

 medioventral cord, both extending the whole length of the trunk. 

 The dorsal cord sinks, in the collar, below the integument, forming 

 tlie collar cord. A capillary network is found within all the limiting 

 or basal membranes of the body. A large contractile vessel lies in 

 the dorsal middle line of the collar and trunk, and a similar vessel in 

 the ventral middle line of the trunk. In the former, the blood flows 



^ In this chapter the author, relying largely upon Spengel's monograph on 

 Balanoglossus, rejects the proposed affinity between the Enteropneusta and the ancestors 

 of the Vertebrata. As this affinity has Ijeen very widely accepted in England and 

 America, the student should consult M'Bride's "Review of Spengel's Monograph" 

 {Quart. Journ. Micro. ScL, vol. xxxvi., 1894), which is written from this latter point of 

 view. — Tr. 



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