Volume /.] October, iSyy. [No. /. 



BIOLOGICAL BULLETIN. 



SOME RELATIONS BETWEEN NERVOUS TISSUE 



AND GLANDULAR TISSUE IN THE 



TUNICATA. 



MAYNARD M. METCALF. 



IT is well known that in the ascidians the definitive brain and 

 the neural gland are both derived from the same region --the 

 trunk region of the central nerve tube of the tadpole. Xhe 

 ganglion is derived from one wall of this tube, and the gland is 

 derived from the opposite wall. Six years ago I pointed out 

 that the ganglion of Salpa is homologous with both the ganglion 

 and the neural gland of ascidians ; the dorsal part of the Salpa 

 ganglion corresponding to the ascidian brain, and its ventral 

 part corresponding to the ascidian neural gland. 1 That is, a 

 certain portion of the embryonic nervous system in ascidians 

 becomes transformed into the neural gland, while in Salpa the 

 corresponding region does not suffer this change, but remains 

 as part of the definitive brain, its cells functioning as gland 

 cells in the adult. I have recently found in the ascidians an 

 interesting series of diverse conditions as to the origin of the 

 gangliated nerve which runs down in the median line of the 

 partition between pharynx and cloaca. 



In this region, the dorsal raphe, one finds a large blood sinus, 

 a muscle (either single or double), a gangliated nerve cord (the 

 rapheal nerve), and frequently a prolongation from the neural 



1 "The Eyes and Sub-Neural Gland of Salpa.," Memoirs from the 

 Laboratory of the Johns Hopkins University. Vol. ii, Part iv. 1893. 



