W. K. BROOKS ON THE GENUS SALPA. 237 



In Plate IX, Fig. 1 is the most proximal section. In this the fertil- 

 izing duct is separate from the follicle, and it has a distinct lumen. In 

 Fig. 9 it is closely adherent to the follicle, but distinct from it, as it is 

 throughout the whole series. In Fig. 10, the most distal section, it is 

 separate from the follicle and solid. In an older egg, Plate X, Fig. 7, the 

 lumen is absent, and that portion of the duct which is distal to each 

 embryo gradually degenerates, as shown at X in Plate X, Fig. 9, and it 

 ultimately disappears completely, while the portion of the duct immedi- 

 ately proximal to each embryo acquires a new opening into the atrium, 

 as shown at 11 in Figs. 9 and 10, and becomes the suspensorium of the 

 embryo, by means of which it is attached to the wall of the atrium, 

 while the other end retains its connection with the follicle. Why it 

 should acquire a new opening into the atrium I do not know, unless it is 

 destined to take part in the formation of the foetal membranes. These 

 are usually regarded as folds of the wall of the atrium (or pharynx) of 

 the chain-salpa, but it is not improbable that a more thorough study 

 of Salpa hexagona and Salpa cordiformis may show that they are 

 actually derived from this portion of the duct. It is certain that they 

 are formed, in all species, from the region where the duct and the wall 

 of the atrium are united, bat I do not think the question of their origin 

 can be regarded as settled. Salensky says that they are derived from an 

 " Epithelhugel " or a raised thickened area, &', in Plate XI, Figs. 1 and 2, 

 which is, according to his account, part of the wall of the pharynx, 

 immediately around the point of attachment of the duct, but it is not 

 at all improbable that the Epithelhugel comes from the duct itself, for 

 if it does not, there does not seem to be any reason why, in species with 

 several embryos, the duct should acquire a new opening for each embryo. 

 I am therefore disposed to believe that the Epithelhugel will ultimately 

 be shown to be a derivative of the duct, although my own material is too 

 scanty to settle the question. 



SECTION 2. Fertilization. 



A ripe unfertilized egg is shown in Plate X, Fig. 1. It lies in a blood 

 space of the chain-salpa, close to the wall 6 of the atrium, and it is usually 

 surrounded by amoeboid blood corpuscles, 12. It is enclosed in a follicle 

 which is one cell thick, and which is simply a distended portion of the 

 duct X. The granular yolk entirely fills the follicle except at the lumen of 

 the duct, but this runs past this egg to the next one in the series. The large 



