2O4 METCALF AND JOHNSON. 



Salpa pnnclata are very broad and flattened, and show in cross- 

 section a slit-like lumen. They are convoluted at their distal 

 apertures (Fig. 16). 



The eyes in the three cyclosalpas, pinnata, chamissonis, and 

 dolichosoma-virgula, show an interesting series of modifications. 

 Figs. 3 and 4, Plate VII., show the character of the large eye in 

 C. pinnata. It is roughly a horseshoe with the ends directed 

 backward, and having an additional mass of optic cells placed in 

 the curve of the horseshoe. This eye has been shown (by Met- 

 calf) to be derived from a horseshoe-shaped eye, like that of the 

 solitary salpa, whose free ends point forward. The position of 

 the eye has been reversed by an actual tipping forward of the 

 whole eye, the ends of the horseshoe remaining attached to the 

 ganglion, while the curved part of the horseshoe swings forward 

 through an arc of 180 (cf. Text-figs, i to 6). The horseshoe 

 shape of the adult eye of the chain C. pinnata is therefore prob- 

 ably in a sense primitive, a reminder of the condition seen in the 

 embryo, which corresponds to that in all the solitary salpas. For 

 a time, however, in the development of the chain C. pinnata the 

 young eye is undivided, there being no split between the lateral 

 halves. This split, which appears later, is probably a reopening of 

 the earlier space between the limbs of the horseshoe seen at a time 

 when in the young embryo the eye had a form similar to that of 

 the eye of the adult solitary salpa. 



Metcalf has shown that the eye of the chain Cyclosalpa cJiainis- 

 sonisis in a condition a little less developed than that of C. pinnata, 

 It is in the form of a flat plate, with no split between its two 

 halves (PI. IX., Fig. 19), though there are two enlargements of its 

 posterior portion, corresponding to the two limbs of the eye of C. 

 pinnata and separated by a furrow which is in the position occu- 

 pied by the split in the eye of C. pinnata. C. cJianiissonis has 

 also an accessory mass of optic cells dorsal to the anterior part 

 of the eye in the same position in which the similar body is seen 

 in C. pinnata (compare Fig. 19, r'" with Fig. 18, p'" and c'"\ 

 The eye of C. chamissonis is either less developed or has reverted 

 to a slightly simpler condition. 



The eye of Cyclosalpa dolichosoma-virgula (PI. VII., Fig. i, and 

 PI. VIII., Fig. 5) is still more different from that of C. pinnata. It 



