544 t. iKEDA : 



tliroiigli ^vllit'll the t'œlomic fluid of the preoral and the collar 

 cavities is j^ut in free circulation. 



A questionable structure has l)een described from the preoral 

 cavity 1)y Mastekman under the name " subneural sinus," and is 

 compared to the structure l^earing the same name in the Hemi- 

 chorda. According to him, the sul)neural sinus is an interstitial 

 space left between the two laminae composing the preoral septum, 

 just under the ganglion and alcove the so-called " subneural gland." 

 Anteriorly and laterally, it is said to be surrounded liy the preoral 

 cavity, and posteriorly, by the collar-cavity ; its upper and lower 

 walls are claimed to be directly formed of the ectoblast without 

 a peritoneal layer. Further it is said, that the sinus connnunicates 

 mid-dorsally with the dorsal blood vessel on the oesophagus. 

 After repeated examinations of the larvœ of the four different types, 

 I am convinced that Masterman's subneural sinus is identical 

 with what I have called the posterior recess of the preoral cavity. 

 It has nothing to do with the tissue-space in the jn-eoral septum, 

 ])ut is clearly a part (jf the preoral Ijody-cavity, which is free 

 from the mesenchymatous fil)res. Besides, I can not in any way 

 detect the presence of the dorsal vessel on the œsophagus, a vessel 

 which connects the suljueural sinus with the dorsal vessel on the 

 stomach. A view similar to mine as above expressed was given 

 Ijy HarmePv in his paper on Cephalodisus ('97)- 



Masteeman has further given an interesting description of the 

 " proboscis pores," situated on each side of the ganglion. They 

 are compared to the proboscis pores of Balanoglossus and are 

 said to fulfill the same function as the collar nephridium of 

 Actinolrocha. In the larvîc studied l)y me, the only things that 

 bear even a remote resemblance t(j them, are the flask-shaped glands 

 which are seen on the upper face of the preoral lobe of the larva 



