614 A. A. W. HUBRECHT. 



The last system that will participate in this metamery is the 

 muscular system, and a rash conclusion — such as is not rare 

 in these days of ontogenetic fetichisra — might lead to the 

 rejection of the views concerning metamery here developed, 

 on the consideration that it is exactly the metamery of the 

 muscular system which appears first of all in the ontogenetic 

 development of Vertebrates. I will not circumstantially refute 

 this argument, but will only remark that in Polygordius 

 and other Chsetopods, which are representatives of a group of 

 animals in which segmentation reaches such a very high degree 

 of perfection, the longitudinal muscular layer of the body-wall 

 is as yet continuous in the adult, and not divided into meta- 

 meric sections, as it is in certain Arthropods and in Vertebrates. 

 Now let us consider contractions of the inner muscular layer 

 of the Nemertea, the only layer that is common to all of them, 

 from Carinella to Cerebratulus and from Cephalothrix 

 to Pelagonemertes. This layer also corresponds with the 

 longitudinal muscular layer just alluded to of other lower 

 worms, such as Polygordius, and, as was noticed in our 

 paragraph on the muscular system, its contraction is some- 

 times very distinct in favorable sections. 



We then see the contraction marked out as so many suc- 

 cessive blocks of contracted, thickened fibres, separated by 

 intervening parts of non-contracted fibrous tissue. The 

 sections demonstrate that the phenomenon persists through- 

 out the whole breadth of the animal, i.e. that successive 

 rings of contractile tissue alternate with intervening rings 

 in which no contraction is observed. This phenomenon is 

 thus in a certain degree comparable to an arrangement in 

 distinct myomeres. 



It is not unimportant that it was especially noticed in the 

 fundamental muscular layer, and it may at the same time be 

 remarked that it appears, from what I have as yet been able 

 to observe myself, that the number of these rings in a given 

 length of the animal is the same, or a multiple of the number 

 of intestinal caeca and transverse nerve-tracts in the plexus ; 

 in other words, that the incipient metamery of the internal 



