372 PROF. E. R. LANKESTER ON CERTAIN POINTS IN THE 
Limulus. Scorpio. 
a.) Plastro-buccals 167. un-seeyise) ne) ee ae Absent: but represented by muscles attached 
to the preoral entosclerite, 99. 
Part iol M025 ta) Me wines jie. See 6. Muscle from subneural part of plastron to 
entochondrite of 2nd mesosomatic seg- 
ment, 86. 
That part of muscle no. 5 between the Ist and) c. Muscle from supraneural part of plastron to 
2nd mesosomatic entochondrites. . . same entochondrite. 
When thus examined in detail a very close correspondence is found between the 
muscles arising from the plastra of the two animals. Perhaps the most important 
conclusion to which we are led by the comparison is that the cartilaginous body known 
as entosternite, entochondrite, or plastron in Scorpio represents the sternal surface of 
one segment J/ess in front, and of one more behind than does that of Zimulus. In 
Scorpion it corresponds to segments 2 to 7 inclusive; in Limulus it corresponds to 
segments | to 6 only. 
There are, no doubt, other relations in which the anatomical facts set forth in the 
systematic descriptions and figures of Mr. Benham and Miss Beck might be considered, 
so as to give them significance. But for the present I must leave this task, and rely 
upon others to make use of some of the many data given in these descriptions. 
Part V. Notes on Certain Points in the Anatomy and Generic Characters of Scorpions. 
By BH. Ray Lanxester. (Plates LX XX. to LXXXIIL.) 
a. The Venous System. 
WueEn I first observed the pericardio-ventral (or veno-pericardiac) muscles of the 
Scorpions, as shown in Pl. LXXX. fig. 15, pp', pp?, &c., and Pl. LXXVII. figs. 1, 
4, & 5; alsoin Pl. LXXVIII. figs. 8 & 9, I discovered that they are to a large 
extent hollow, being excavated funnel-wise both at their pericardial attachment and at 
their insertion into the wall of the venous sac-like dilatation which surrounds the in- 
sunken lung-book (see the sections, Pl. LXXIX. fig. 10, and Pl. LXXXI. fig. 2, ppm). 
I was led to think it possible that these hollow muscles formed a direct channel of commu- 
nication between the pulmonary venous sacs and the pericardium, the blood being returned 
through them to the heart in an aérated condition. Although similar muscles exist in 
Limulus, the channel which the blood pursues on its way from the gills to the heart is 
quite independent of them, and in Limulus they are solid. This led me to attempt, by 
