320 A. T. MASTBRMAN. 



represented in Actinotrocha by the atrial grooves already 

 described. 



Stomach. — After the pharynx is found the digestive por- 

 tion of the stomach ; and though the intracellular digestive 

 areas may be probably regarded as the first rudiments of the 

 hepatic diverticula of Bala noglossus, this suggestion cannot 

 be enlarged upon here. 



Intestine and Anus. — An intestine suspended by a ventral 

 mesentery terminates in each case in a posterior anus. 



Mesodermic Organs. 



Vascular System. — As in the case of the nervous system, 

 the vascular tissues in both Balanoglossus and Actino- 

 trocha are in what is undoubtedly a primitive condition. 

 The veins and arteries, in fact, are merely sinuses and chinks 

 between the mesoderm on the one hand and the ectoderm or 

 endoderm on the other. 



In each case (figs. 50, 51) there is a large sinus (the sub- 

 neural sinus \_s. n. s.] of Actinotrocha, the heart [ht.'] of Bala- 

 noglossus), which lies just below the junction of pre-oral lobe 

 and collar, a position with a special significance. This is con- 

 tinued along the dorsal eudodermic wall between the collar 

 walls as a small fissure into a larger sinus, with more or less 

 muscular walls, differentiated from the trunk coelomic walls, 

 which are produced forward (perihtemal, Spengel). In each 

 case there is a ring sinus in the collar-region which is con- 

 tinuous with a ventral median sinus below the gut. Such 

 resemblances, in so plastic and adaptable a system as the 

 vascular, speak for themselves (cf. figs. 48 and 49). 



Coelom. — The condition of the coelom in Actinotrocha 

 bears so remarkable a resemblance to that of Balanoglossus 

 and Cephalodiscus that a genetic relationship might be 

 claimed upon this count alone. 



The pre-oral lobe is in each case lined internally by the 

 mesodermic wall of the pre-oral coelom, the cavity of which 

 is itself partially filled by muscular tissue, passing in various 

 directions, though in each case the main strands can be 



