Royal Microscopical Society. 259 
discerned ; and its structure is thus seen to conform to ordinary 
types. 
In Plate XL., a portion of the valve of Eupodiscus Argus is 
shown as seen in the manner described. No figure of Isthmia is 
given, because, though enough was seen to justify the preceding 
remarks, some important points in the arrangement of the minute 
spherules were left in doubt. 
IV. — Notes on the Development of the Nervous System of the 
Annulosa. By B. T. Lowne, M.B.C.S., F.L.S., Lecturer on 
Physiology at Middlesex Hospital Medical School. 
( ILcid b fore the Royal Microscopical Society, Nov. 6, 1872.) 
Plate XL. (Lower portion). 
A year and a half ago (January 11, 1871) I had the honour of 
reading a paper before you “ On the Anatomy of Ascaris lumbri- 
coidesf and I then ventured to express the opinion that the nervous 
system of the Invertebrata is developed, like that of the Vertebrata, 
from the serous layer of the blastoderm. I had at that time set 
myself the task of working out the subject, but time has not sufficed 
to do what I had wished, and as a year or more may yet elapse 
before I have worked out this interesting matter, I have been in- 
duced to give you a resume of what is at present known on this 
head, and to furnish you with the principal facts which have led 
me to believe that such is really the case. 
In June, 1871, Hr. E. Metschnikoff published an essay in 
Kolliker’s ‘ Zeitschrift ’ on the development of scorpions, which has 
confirmed my opinion, as his observations are a connecting link 
between my own as yet imperfect researches. This essay changed 
what was little more than suspicion in my mind into a strong belief. 
DESCRIPTION OF PLATE XL. (Lower portion). 
Fig. 1. — The ventral surface of an embryonic scorpion, showing the chain of 
ganglia, a a, on either side of the primitive furrow, one being situated 
at the base of each appendage. After Metschnikoff. 
,, 2.— A transverse section through one of the ganglia and lateral appendages 
of a younger embryo, a, ganglion in the epiblast ; b, rudiment of a leg 
outside the ganglion ; c, mesoblast ; d, hypoblast. After Metschnikoff. 
„ 3. — The extremity of the abdomen of a scorpion embryo, showing the splitting 
of the mesoblast to form the body cavity, a', epiblast ; c, mesoblastj 
d, hypoblast ; e, body cavity. After Metschnikoff. 
„ 4.— A section of the entothoracic epiphysis of the mesothorax of a fly, showing 
its relation to the nerve ganglia, a, process of integument ; b, nerve 
centre bound down to the thorax ; c, nerves passing from it. 
