114 A. OKA. 



underside with the ceiliu^^. As seen in cross sections, they are more 

 closely set nenr the edg-e and abnost entirely wanting in the central 

 part of the epistouie. 



6. Nervous System. 



This system has been described more or less fally in all works 

 on Polyzoa, but the accounts given are very difterent from my own 

 observations. Xearly all investigators describe the cerebral ganglion 

 ns a solid cellular mass. Nitsche, studying the process of gemma- 

 tion, states that the ganglion has at first a ventricle, which, however, 

 obliterates with the growth of the animal. Contrary to this state- 

 ment, Saetftigen (10) recently discovered that in Gristatdla and 

 Pliuiiatclla, the cavity of the ganglion persists throughout life, and 

 further that the ganglionic wall is not everywhere of the same 

 thickness, being at some parts as thin as the lining epithelium of the 

 body- walk I have observed that in rcctinatdla also the cavity 

 exists in the mature state ; it is so very large that at first sight it 

 might be mistaken in sections for a part of the body-cavity. 



In tig. 28, PI. XrX, I have represented the form of the ganglion 

 in Pedinalella (jclatiiwsa. It may be compared with a spindle bent 

 somewhat in the fjrm of U, and fitted with its concavity to the anal 

 side of the œsophagus, in rather an oblique position with the arms 

 turned slightly upward. The end of each arm again makes a sharp 

 bend in the anal direction and is continuous with a large ner^•e trunk 

 which proceeds into each hjphophoral arm. The ganglion is in 

 direct contact with the inner cell-layer of the œsophagus, the outer 

 layer of that tube enveloping it on all other sides ; the ganglion is in 

 fact situated between the two layers of the œs(.)})hagus (fig. 29, PI. 

 XIX). The lophophoral nerve trunks are likewise located between 



