( 501 ) 

 as vve fee the fmalleft membranes to be in the bodies of animals, we 

 muft again exclaim, " what inconceivable minutenels is here !" 



Moreover, I cut a Rufh tranfverfely, in as thin a flice as I was able, 

 that I might the better conceive the formation of what' I have cal- 

 led the afcending blood-veflels, and bring them into A'iew. 



jP/^. 36, A B C D E F G H I K L M N O P, reprefents a fmall piece 

 of RuHi cut tranfverfely. In E F K L S, is fliewn, as nearly as the 

 engraver could reprefent it, one of the before mentioned valves 

 or diviiions which are fhewn in Jig. 33, atEFGHIK, and, as I 

 have before faid, oppofe the entrance of water and give rtrengtli to 

 the Ruili. This formation conlills of an incredible number of vef- 

 fels and mebranes, each veflel being in a contrary pofition from that 

 adjoining to it. This valve or divilion has five diliindt fides, as at 

 S E, E F, F K, K L, and L S, and thus (as I have before faid) al- 

 mofi: all the tubes in the Rufh are formed. 



Now let us fuppofe one fide of the tube in the Rufli, which in 

 fig. 34, is defcribed at L M N Q, to be the fame as the fide which 

 is reprefented cut acrofs, in Jig. 36 atLM; and moreover, that 

 in fig. 34, NOPQ, is another fide of the fame tube, fliewn in 

 fig. 36, at MN, and alfo, that what I have called a blood- veflel, 

 and reprefented in fig. 34, at NQ, is the fame with fig. 36, where 

 an oval hole is £hewn between M and O, and that this veflel is cut 

 acrofs. 



Having made thefe obfervations, and moreover, feeing that in 

 various cavities of the large tubes of the Rufli, there were formed 

 many membranes, efpecially when the Rufli began to be fo thin, a§ 

 is fliewn in the partition of two of the tubes in ^g-. so^ between 

 D E S R and D R Q C. I concluded that the fides of the large 

 tubes in the Rufli were formed of the fmall afcending tubes, which 

 I call blood-vefl"els, as follows : 



From the afcending veflels placed between B P Q, the fides of the 

 veflels P O, Q. R, B C, B A, and P T, are in part formed ; and 

 alfo from the afcending veflTel placed in R, in part is formed the 

 fide of the tube, R Q. 



