NOTES ON THE STRUCTUEE OF OIKOPLEURA. 35 



size of the lateral testis lobes which now no longer invade 

 the dorsal part of the body ; these figures (PI. I. figs. 7, 9, 

 10) also show the increase of the dorsal cap of large 

 ectoderm cells and of test both in thickness and in super- 

 ficial extent. About the 70th section (PI. I. fig. 10) it may- 

 be noticed that the test is becoming thinner in the medio- 

 dorsal line and thicker in its lateral parts. The most 

 posterior (curved) part of the nerve cord (myelon) is seen 

 in figs. 9 and 10. Its two ends diverge, the one {n.s.) 

 dorsally and to the right to become continuous anteriorly 

 with the cerebral ganglion, and the other {n.) ventrally and 

 to the left to join the caudal ganglion and nerve (compare 

 PL IV. fig. 9,71.). 



Ten sections further forward (PL 11. fig. 1) the cardiac 

 and pyloric sacs are found to join at their dorsal ends, and 

 from this point forward to its anterior extremity, in section 

 163 or so, the stomach is seen as a single cavity which 

 gradually diminishes in its vertical and increases in its 

 horizontal (lateral) extent. The oesophagus is still seen 

 running forwards over the stomach dorsally, and the cilia 

 and gland cells are distributed as before. After another 

 ten sections we find that the two lateral testis lobes 

 become connected by a median band immediately above 

 the much reduced ovary w^hich now bifurcates (PL II. fig. 

 2) and then dies away. This last figure shows the con- 

 striction marking the separation of the intestine (i) off 

 from the pyloric sac. 



We now come to the point where the oesophagus passes 

 into the pharynx or branchial sac, and in section 103 (PL 

 II. fig 3, ph.) it is seen that the lumen of this dorsal cavity 

 has become distinctly triangular with a medio-dorsal 

 groove which is the posterior end of the well marked 

 epipharyngeal groove corresponding to the dorsal lamina 

 of Ascidians. The stomach and testis are much as before, 



