AN T AUSTRALIAN CHAKTOGNATH — JOHNSTON. 255 



The ccelomic epithelium lines the inner surface of the muscle 

 as a single celled layer. It is present on the mesentery and 

 forms the ccelomic lining of the alimentary canal. 



This canal extends as a simple wide tube from the slit like 

 longitudinal mouth to the anus situated just behind the junction 

 of the body and tail. There are no diverticula in the neck 

 region. The mouth and anus are both ventral. The wall of 

 the digestive tube consists of a single laj'er of columnar cells, 

 the enteric epithelium covered on the outer side by the coelomic 

 epithelium. 



The intestine is suspended by the dorsal and ventral inesen- 

 teiips. Thus the body codome is divided into two parts longi- 

 tudinally. The tail ccelorne is similarly divided. The anterior 

 septum, dividing the head ccelorne from that of the body, passes 

 forwards laterally. Tlie tail septum is well marked and projects 

 behind the anus into the tail, consequently it •appears in a trans- 

 verse section of the anterior end of the tad (PI. lxxi., fig. 8). 



The gonads are well developed in the type, but are longer in 

 one of the smaller specimens. The ovaries extend forwards about 

 as far as the anteiior end of the posterior fin, a little beyond it 

 in some cases. They are apparently not attached along the 

 middle of the lateral border but just ventrally to it. This may 

 be the result of some distortion, though I do not think so. The 

 oviduct is on the outer edge of each ovary, and terminates later- 

 ally at the junction of the body and tail. The mature ova are 

 spherical, measuring 0"24 mm. in diameter. 



The testes are located in the anterior and lateral part of each 

 tail ccelorne, their length being about 1 - 5 millimetres. Sperm 

 morula? averaging 0"(M mm. in diameter fill this ccelorne. The 

 vasa deferentia are small, but each terminates in ripe animals in 

 a large prominently projecting vesicula seininalis As mentioned 

 before, neither the posterior tins nor the tail fin reach these 

 structures, which are situated about IT mm. in front of the 

 extremity of the tail. 



The detailed histological structure of some Chaetognaths is 

 described frilly by Dr. O. Hertwig. 12 



The main characters of this species, for which the name 

 Sagitta austrdlis is proposed, may be summed up thus : — Head 

 rather small; neck distinct ; no collarette; body transparent and 

 flabby, thickest in the posterior third, tapering gradually for- 



12 Hertwig — Die Chsetognathen. (Jenaische Zeitschr. Med. und 

 Naturwiss., xiv., 1880, p. 196.) 



