SALPIDA. 



51 



Later it becomes solid and detached from the pharyngeal diver ticulum, 

 which persists as the ciliated pit. The two subneural glands arise as 

 two invaginations of endoderm further back where the ganglion is in 

 contact with the pharyngeal epithelium. The elaeoblast (Fig. 43, eb) 

 is a mass of apparently large mesodermal cells in the nucleus in later 

 embryonic life. The large cells of which it consists are filled with 

 nutritive matter, and it is probably to be regarded as reserve of food 

 material. A similar tissue is found in the stolon of Pyrosoma. By 

 Salensky it is regarded as a vestige of the tail and notochord of a 

 larval stage. 



The stolon makes its appearance in the embryo as a diverticulum of 

 the ventral wall of the pharynx between the end of the endostyle and 



FIG. 43. Late stage of the embryo of Salpa democratica-mucronata (after Salensky from Kor- 

 schelt and Heider). e atrial aperture ; eb elaeoblast ; ed intestine ; es endostyle ; ft ciliated 

 pit ; i mouth ; k gill ; m stomach caecum ; n ganglion ; oe oesophagus ; p pericardium ; pi 

 placenta ; st stolon ; t basal plate of placenta. 



the opening of the oesophagus (Fig. 43, st). This soon raises the ectoderm 

 and a small process of the ventral body- wall is formed projecting into the 

 tunic. As this process lengthens a cavity appears between it and the tunic, 

 and acquires an opening to the exterior so that the young stolon lies in a 

 tube formed by the tunic. In some species this tube is directed straight 

 forwards along the ventral side of the body (Cyclosalpa pinnala, Salpa 

 affinis, etc.). In others it is at first directed forwards, then turns to the 

 left and runs backwards on the left side of the nucleus, opening behind 

 this organ (lasis tilesii, etc.). In yet others (Fig. 39) the tube winds spirally 

 round the nucleus (Thalia democratica-mucronata, etc.). With later growth 

 the stolon extends beyond this tube and projects freely uncovered by tunic. 

 Later on the zooids produced on the stolon acquire tunics as a result of 

 their own activity. The projecting part of the chain of zooids is usually 



