( Ixiii ) 
card along with the specimen) appears to be that of a quite 
normal ¢. An injury to the creature in its larval state 
might have produced a false appearance of segmentation on 
the right side of the 2nd dorsal plate, so that what has been 
called half-dorsal plate 3 might be really only a part of the 
2nd abdominal segment. But in that case the lateral hook 
which should characterize the 6th segment must be supposed 
to have been transferred to the 5th segment, the apical teeth 
of the 7th segment to have been developed on the 6th, and 
the 7th segment itself to have disappeared altogether on the 
right side, a state of things which seems quite inconceivable. 
The aspect of the specimen suggests rather that the whole 
right half of its dorsal surface after the 2nd segment has 
been somehow forced backwards towards its head, the right 
half of dorsal plate 3 having been separated from the left half 
and afterwards attached to and incorporated with the left half 
of the preceding segment, the right half of segment 4 similarly 
quitting its own corresponding left half and joining the left 
half of segment 3, and so on. 
The exhibitor then invited expressions of opinion on the 
question whether this malformation had originated in the 
larval stage or in the embryo, and handed over the specimen 
to the President for presentation to the Teratological collection 
in the National Museum at South Kensington. 
Dr. T. A. Cuapman said this malformation had clearly no 
causation in any larval injury, but dated from an early period 
of embryonic life. It arose when the flanks of the embryo 
closed dorsally (venter of vertebrates) over the visceral cavity. 
At about the 4th abdominal segment, two segments on the 
right side had met one on the left, and thrown out the correct 
apposition of the remaining ones, the 7th right uniting dorsally 
with the 6th left and soon. Such an accident looked a very 
probable one to occur, yet it is certainly extremely rare, and 
he did not know whether others were on record. It was 
difficult to conceive any external interference occurring to 
produce it ; and if this were not possible, it must arise by the 
margin of one segment failing at this early period to attain its 
full width. This no doubt explained the rarity of the mon- 
strosity, as the period during which things have gone correctly 
