CRANGON VULGARIS. 21 



the Compound Eye of Crangon ( J 86a)and that the invagina- 

 tion or inpushing which I there described as giving rise to 

 the ommatidial layer of the eye, in reality gives rise to the 

 ganglion of the eye which in the adult is contained within 

 the ophthalmic stalk. It forms the anterior outer portion 

 of the tract lettered "oZ"in figures 11, 12, 28, 32, etc. Be- 

 hind, and nearer the median line a second ganglion is 

 formed(<7 1 , in figures 33 and 34) which is clearly preoral and 

 is as clearly not connected with the first antenna, which 

 appendage is still distinctly behind the mouth. This, I re- 

 gard as the primitive prestomial ganglion, equivalent to the 

 supra-o3sophageal ganglion of the annelids. 1 Behind the 

 mouth(fig. 35 na)\s shown a somewhat paired ectodernial 

 thickening which is clearly the ganglion of the antennula. 

 Sections passing through the second appendage show a con- 

 dition of affairs essentially the same. 



None of my transverse sections of stages D, E and F, 

 proved satisfactory, and between stages O and G, many 

 changes occur which can be but imperfectly studied in my 

 drawings of the external appearance (figs. 1418) and in 

 the longitudinal sections represented in figs. 38 and 41. 

 In stage J5, fig. 14 shows an " optic lobe" (ol) which, from 

 the preceding paragraph, is seen to be made up of optic 

 elements #nd an optic ganglion proper a primitive supra- 

 oesophageal ganglion (o^)and two ganglia(s^and one behind 

 it, unlettered), belonging to the two pairs of antennae. In 

 a longitudinal section of the same stage (fig. 38) it is seen 

 that the prestomial region of the nervous system (og) has 

 considerable longitudinal development while behind the 



1 Owing to the fact that my drawings were made at different times, 

 and that my views on the development of the nervous system have 

 undergone serious alteration during the progress of my studies, there 

 will be found some confusion in the reference letters in the plates on 

 those parts that refer to the brain. In the text I have endeavored to 

 straighten this. 



