378 WILLIAM PATTEN. 



pair of tlioraeic legs ; the double-lobed ueuromeres ; the four pairs of rudi- 

 mentary vagus appendages, v. p^~*. ; and the bundle of nerve-fibres lying in 

 the skin from which the spinal nerves are developed, sp. n. 



PLATE XXIV. 



Fig. 3. — Stage e : surface view of detached embryo of the Scorpion. The 

 left side of the head is represented as an opaque object, and shows the growth 

 of the optic ganglia over the brain-segment, and the advance of the lateral 

 lips of the ganglionic invagination over the optic ganglia. The right side is 

 represented as transparent ; the dotted line, e. s., shows the form of the sac, 

 the outer wall of which is formed by the eye ; the frontal, now nearly semi- 

 lunar lobe, s. I., lies beneath the brain and optic ganglia, op. (/". and op. tp". 

 We also see the position of the coxal sense-organs indicated at c. s. c"., al- 

 though 1 have not been able to detect them in surface views ; the appendage- 

 like maxillaria, mxl., in the third and fourth thoracic segments ; the double 

 neuromeres, the anterior portion of each containing in the median line a very 

 distinct pit-like invagination of the median furrow, g. m. c. ; the posterior 

 portion, a very small and indistinct one, the intergangliouic portion of the 

 median furrow, i. m. c. ; the four lung-books, /. b^-'^., the first one belonging 

 to the last vagus segment, the rudimentary appendage of which has dis- 

 appeared. 1 have found no evidence that it is infolded to form the lung-book, 

 the development of this lung-book being the same as the following segments 

 where no appendages are ever present. 



Fig. 4. — Stage f : surface view of a detached embryo of Scorpion, showing 

 the almost complete union of the two optico-ganglionic sacs ; the lateral eye- 

 plates, /. e. ; the numerous sensory buds, s. o^., scattered over the surface of 

 the segmental sense-organs, s. s. o. There are also usually one or more quite 

 large sense-organs on the basal joints of the appendages, s. o^. The first three 

 vagus neuromeres have completely fused with one another, but the fourth is 

 still quite independent. 



N.B. — The Scorpion referred to in the present memoir is probably Buthus 

 carolinianus. 



