pericordium 

 glomerulus 



heart nervous layer of epidermis 



ciliated funnel and 



muscle fibers 



coetom II 



dorsol blood vessel ■ i j 



dorsal nerve cord 



dorsal mesentery in coelom III 



passage for 

 pharyngeal open 



pharyngeal pore 



coelom 



stomochord 

 ventral mesentery mouth 



'\ protosome 



_ — pharyngeal ridge, 

 ^oesophageal passa 



blood vessel-' 



collar 



enfrol nerve cord 



entral mesentery tongue boi 



pore of coelom 

 dorsal blood sinus 



coelom 



skeleton 



nervous layer of epidermis 



dorsal blood vessel. 



vessels of genital v/ing 

 perihaemol space 



pore pharynx 



tongue boi 



circumenteric vascular channel 



dorsal nerve cord 



gonad 



muscle fibers' 



digestive pharynx 



ventral nerve cord 



Figure 1-11. Anatomical details of enteropneusfs. A, median sagittal section of anterior end of 

 body, not identified as to genus; B, diagrammatic section of body wall showing relationships of pouches 

 to pharynx and the subdivision of the latter by a fold; C, cross section of protosome-mesosome 

 junction area; D, cross section through anterior part of metasome. (After Dawydof?, 1948) 



Posterior to the pharynx the esophagus may be short and 

 not sharply differentiated; in Saccogiossus it opens to the ex- 

 terior through several pairs of dorsal canals. The intestinal 

 walls are ciliated. Anteriorly there are pairs of dorsolateral 

 hepatic diverticula. These pouches arc richly supplied with 

 blood and have a pigmented, glandular epithelium. Behind 

 the hepatic diverticula, the walls of the intestine are folded. 

 There may be dorsolateral ciliated grooves, with longer 

 cilia than elsewhere, or a single groove on the left. 



Each of the three body segments has coelomic cavities; 

 those of the first two segments open to the exterior through 

 ciliated funnels. There is only a single protocoel funnel in 

 some forms (Figure 1-1 1). The cavities of the collar (meso- 

 coel) and metasome (metacoel) are paired, as indicated by 

 a midline septum. The coelomic spaces are not obviously 

 lined, for much of the mesoderm takes the form of the smooth 



muscle fibers that criss-cross the cavities or form longitudinal 

 bands. Loose connective tissue (mesenchyme) may fill parts 

 of the cavities. 



There is no notochord in this group. The buccal divertic- 

 ulum has been assumed to be a rudimentary notochord 

 because it is an outgrowth from the ''gut." However, it lies 

 ventral to the dorsal blood vessel and below it lies a small 

 skeletogenous plate. These are not the relationships of 

 a true notochord. From the skeletogenous plate, crura, or 

 processes, extend back to either side of the mouth tube. This 

 skeleton is formed of laminated collagenous material. Skele- 

 tal rods are also associated with the U-shaped inner pharyn- 

 geal openings (Figure 1-12). 



The nervous systems consists of an epidermal plexus or 

 network of fibers in which there are main tracts. The dorsal 

 cord is invaginated in the collar region to form a tube or a 



THE PROTOCHORDATES 



13 



