372 PEOF. E. B. LANKBSTER ON CERTAIN POINTS IN THE 



Limulus. Scorpio. 



a. Plastro-buccal, 67 Absent : but represented by muscles attached 



to the preoral entosclerite, 99. 



Part of no. 5 ? b. Muscle from subneural part of plastron to 



entocbondrite of 3nd mesosomatio seg- 

 ment, 86. 

 That part of muscle no. 5 between the 1st and 1 c. Muscle from supraneural part of plastron to 

 2nd mesosomatic entochondrites . . .J same entocbondrite. 



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, entocbondrite, or plastron in Scorpio represents the sternal surface of 

 one segment less in front, and of one more behind than does that of Limulus. In 

 Scorpion it corresponds to segments 2 to 7 inclusive ; in Limulus it corresponds to 

 segments 1 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. 



Pabt V. Notes on Certain Points in the Anatomy and Generic Characters q/ Scorpions. 

 By E. Ray Lankester. (Plates LXXX. to LXXXIII.) 



a. The Venous System. 

 When I first observed the pericardio-ventral (or veno-pericardiac) muscles of the 

 Scorpions, as shown in PI. LXXX. fig. 15, pp^, 2^2^^, &c., and PI. LXXVII. figs. 1, 

 4, & 5 ; also in PI. 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, PI. 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 aerated 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 



