ENTEROPNEUSTA 



377 



passes from the fore-gut to the gill-pockets, and from there 

 to the outside world by means of the dorsal pores. ^ 



The intestine also presents paired dorsal evaginations in 

 the parts which lie behind the gill region. These are the 

 hepatic appendages. They also influence the shape of the 

 body, inasmuch as they cause the skin to protrude (Fig. 

 164), and the musculature is only slightly developed at 

 these places. The hindermost portion of the intestine lacks 

 the appendicular structures, and extends straight to the 

 anus. 



One mesentery extending in the dorsal and another in the 

 ventral line serve for the attachment of the intestine. By 

 means of the mesenteries the body cavity is divided into a 

 right and a left portion, but the two parts are confluent in 

 many species, owing to the 

 perforation of the dorsal 

 mesentery. The body 

 cavity of the collar is dis- 

 tinct from that of the 

 trunk, and also differs 

 from it in its mode of 

 origin ; moreover, it is for 

 the most part reduced by 

 being filled with connec- 

 tive tissue and muscula- 

 ture (Fig. 165). In the 

 tx'unk, on the contrary, 

 the greater part of the 

 body cavity is said to 

 persist, and its wall is 

 composed of the longi- 

 tudinal and circular mus- 

 culature of the somatic 

 and splanchnic layers (Spengel). However, according to 

 other statements, even the trunk cavity is said to lose the 



Fig. 166. — Transverse section through 

 the branchial region of Balanoglossus rainu- 

 tux (after Spehgei). d, intestine ; db, 

 dorsal blood-vessel; dn, dorsal nerve; 

 g, genital organ; fc, gill-pockets; Ih, body- 

 cavity; p, pore of the gill-pockets; so, 

 somatic, sp, splanchnic, layer of the meso- 

 derm ; vh, ventral blood-vessel; vn, ven- 

 tral nerve. 



1 [A full account of the very complicated structure of the gills is given 

 in Spengel's monograph (No. VI.), to which we particularly call attention 

 in the matter of this and other anatomical conditions, and especially in 

 view of the correction which it has since undergone.— K.] 



