22 M. Mohl on the Structure of Annular Vessels. 



rection ; but that, in general, at the point of junction of the 

 two fibres the annular fibre does not become thinner, the 

 spiral fibre being attached only to the lateral edge of the an- 

 nular fibre, which preserves an uniform thickness throughout 

 its entire extent (fig. 1, 9, 10). There are even instances in 

 which this union does not take place in the direction of the 

 spiral, but where the spiral fibre terminates in two divergent 

 branches (fig. 10 a, CommeUna tuberosa) separating right and 

 left, and confluent with the annular fibre. 



An examination of the proportions above mentioned, be- 

 tween the annular fibres and the spiral fibres which unite 

 them, must excite doubts of the accuracy of Schleiden^s 

 theory of the origin of annular vessels. In fact the division 

 which takes place in many rings is, as we have seen, nothing 

 less than a proof of the ring being composed of the two 

 united fibres of a spiral fibre ; whilst, on the other hand, the 

 direction of this division parallel to the edges of the rings 

 is quite opposed to Schleiden's theory, and shows us that, in 

 these more or less divided rings, we see a transition from the 

 simple ring to two rings, situated at considerable distances 

 from each other. An organization entirely analogous is also 

 found in the spiral fibre, for there are spiral vessels traversed 

 in the middle by a narrow fissure (fig. 4, 6, CommeUna tube- 

 7'osa), by which the decomposition of the simple spiral fibre 

 into two fibres placed at certain parallel distances is indicated. 



What chiefly militates against the formation of rings by the 

 united spiral coils of a spiral vessel, is the proportion which 

 the rings bear to the spiroi'd fibres which unite them. And 

 first, when the organization of the vessels is very regular, 

 the rings and the fibres are generally of the same width 

 (fig. 4, 9), which could not be the case if the rings were com- 

 posed of a double twist of the fibre. If then the spiral fibres 

 which unite the rings are slender, the width of these fibres 

 bears no exact proportion to the width of the rings and of 

 the divisions perceived in them (fig. 1) ; moreover, the fibres 

 are sometimes soldered to the rings, and sometimes separated 

 from them. The spiral fibres, when they are united to the 

 rings, cannot be considered in certain cases, and according 

 to the form of the point of union, as a part of the fibrous mass 

 which forms the ring, this part separating from the ring, and 

 continuing in a spiral direction. 



I have thought it right to explain these considerations, in 

 the first instance, upon the annular vessels in a state of com- 

 plete development, because observations made on developed 

 vessels are necessarily more precise and certain than those 

 made on yoimg vessels ; not so much on account of the larger 

 size of the developed vessels, but because, in consequence of 



