from the South Pacific. 271 



of the fine setae scattered over its surface or arranged in fasci- 

 cles which have been observed in Sagitta hipunctata and other 

 allied species • it is possible, however, that these latter were pre- 

 sent when the animal was alive, their extreme tenuity and their 

 slender attachment to the surface of the integument rendering 

 them exceedingly liable to become detached. One specimen, 

 when submitted to dissection, exhibited most clearly tlie pe- 

 culiar and characteristic nervous system described by Professor 

 Huxley, and which induced that eminent comparative anato- 

 mist to refer this aberrant genus to the Annulose section of 

 the Invertebrata, and to consider it most closely allied to 

 the Annelida in that section. This nervous system consists 

 essentially, in the first place, of a single ganglion lying- 

 in the abdominal region, from which proceeds both forwards 

 and backwards a pair of lateral chords, the posterior ones ter- 

 minating separately in fimbriated extremities, and the anterior 

 ones uniting with each other above the oesophagus so as to 

 form an hexagonal cerebral ganglion, which gives off two 

 processes, said by Krohn to terminate in the muscles which 

 effect the motion of the falces, and tAvo others which, passing 

 backwards for a short distance, dilate at their extremities and 

 form the optic ganglia. 



The ovaries in the specimens examined were very large 

 and distinct, measuring in one instance one-third of the entire 

 length of the animal's body, and demonstrated moreover that 

 the animal had arrived at its adult condition. 



Since Mr. Busk published his monograph of the genus, 

 already referred to, he has also recorded, in the pages of the 

 same journal (1858), the particulars of the development of this 

 interesting genus, as elucidated by the researches of Gegen- 

 baur, but which had previously been involved in much obscu- 

 rity. That astute naturalist, by confining pregnant indivi- 

 duals of 8. hipunctata and other species from the Mediterra- 

 nean in glass receptacles, obtained ova which were found to 

 develope immediately into the adult form without undergoing 

 any metamorphosis. These ova or spawn were enclosed in a 

 common gelatinous investiture, and in this respect likewise 

 showed their aflinity to the Annelida rather than to the Mol- 

 lusca, of which latter class, in the earlier part of their history, 

 the SagittcR had previously been looked upon as aberrant 

 representatives. 



Subjected to a high power of the microscope, the edges of 

 the falces of S. tricuspidata are found to be perfectly smooth 

 and entire, and this in contradistinction to those of S. serrato- 

 dentata, of which the inner edges are described as being 

 serrated for about one-half of their length. 



