XYII 



PEOTOCHOEDATA 



575 



hemispherical pockets of clear cells, each cell terminating in a conical 

 spike. Between the two eye-cups were a mass of pigmented cells. 

 At the hase of the apical plate a mass of nervous fibrils could be seen 

 (Fig. 419). 



In somewhat older larvae a sohd mass of cells could be seen lying 

 in the blastocoele, above and somewhat to the right of the proboscis- 

 pore. These cells, whose origin Morgan could not determine, we 

 conclude, from the development of Dolichoglossus, have been derived 

 from the posterior wall of the anterior coelom. They are the rudi- 

 ment of the pericardium, for in a slightly older larvae they became 



Fig. 419. — Illustrating the structure of the apical plate and eyes of a full-grown 

 New England Tornaria larva. (After Morgan.) 



A, apical -vaew of full-grown Tornaria, sliowing tlie apical plate and eyes, and the relation of the plate 

 to the longitudinal ciliated band. B, antero-posterior longitudinal section through the apical plate and 

 eyes. cU.long, longitudinal ciliated band ; muse, muscle cells belonging to the apical string ; oca, 

 anterior eye ; ocp^ posterior eye. 



hoUowed out to form a vesicle (per, Fig. 421). Between this vesicle 

 and the oesophagus and the posterior wall of the anterior coelom there 

 existed a V-shaped space, fiUed with blastocoehc fluid ' and opening 

 into the blastocoele behind. This space is the rudiment of the pecuhar 

 dorsal heart of Balanoglossida, which has been seen to pulsate. 



In larvae older than the second stage described, the posterior 

 or trunk coelomic cavities could be seen developing exactly as 

 Heider described in the case of Balanoglossus clavigerus. SMghtly 

 later, the middle or collar coelomic cavities originated as solid 

 evaginations of the posterior part of the wall of the stomach (Fig. 

 420). Both pairs of rudiments, after being cut off from the alimentary 



