vol. 2, pt. 2.] A TAXONOMIC STUDY OF THE SALPIDAE METCALF. 



19 



1899). In some other species they are clearly glandular, forming 

 the secretion by proliferation of cells from the epithelium and their 

 degeneration. 



In the Salpidae the neutral glands arise from the epithelium of the 

 pharyngeo-atrial chamber, in a manner described by Metcalf (1892, 

 1893, b and c). This is entirely different from the neural gland of 

 Ascidians and Pyrosoma, which arises from the wall of the neural 

 tube. The gland in Ascidians and Pyrosoma opens into the dorsal 

 tubercle by a duct which is the persistent anterior end of the nerve 

 tube. In the Salpidae the neural glands have never at any time any 

 connection with the dorsal tubercle or the nerve tube, its ducts, like 

 the glands themselves, coming from the epithelium of the pharyngeo- 

 atrial cavity. There seems, 

 at first thought, no ground 

 for any homology between 

 the neuralglands in Salpidae 

 and the neural glands of 

 other Tunicates, and we have 

 no fully convincing reason 

 for believing their functions 

 to be the same. But com- 

 mon function and true ho- 

 mology between the glands 

 of Salpa and the gland of 

 Ascidians is suggested by 

 the conditions in Ascidia 

 mammittata and some of its 

 nearest relatives, in which the very slender and greatly elongated duct 

 leading from the neural gland to the ciliated funnel 1 is much branched 

 laterally, these branches connecting with the pharynx by small 

 ciliated funnel-shaped pores. In these forms, the neural gland opens 

 to the pharynx by the ciliated funnel proper and also by very numer- 

 ous lateral pores. 2 In other Ascidians the neural gland opens only 

 by way of the ciliated funnel. Embryonic Salpas and young buds 

 have the neural tube opening forward into the ciliated funnel, but they 

 have no neural gland. Later the neural tube closes and its connec- 

 tion with the ciliated funnel is lost. Then a new type of neural gland, 

 as described, developes from the pharyngeo-atrial epithelium. This 

 may have arisen ancestrally from structures like the lateral ducts 

 and pores of the neural gland in Ascidia mammitlata and its relatives. 

 In Octacnemus, which Hcrdman (1888) has placed among the Salpidae, 

 I found the neural gland to be wholly of the Ascidian type. This is 

 one of several features in its structure that have led me to count 



Fig. 8.— Cyclosalpa pinnata, aggregated form, a trans- 

 verse SECTION THROUGH THE VENTRAL HALF OF THE GAN- 

 GLION, THE NEURAL GLANDS, AND THE OUTGROWTHS FROM 

 THEGANGLION. X 130 DIAMETERS. FROM METCALF (1893, C). 



1 This is really the anterior end of the nerve tube. 



5 Sec Metcalf (1900), section 1. 



