AND THE LOWER ANIMALS. 35 



have we ever found the slightest trace of a cellular 

 formation in either of these structures.* 



There cannot be the slightest doubt in regard to 

 the non-cellular character of the muscular tissue. 

 We have seen entire apparatus, fully formed, and 

 quite perceptible, yet composed of sarcode alone. In 

 certain mollusks, the digestive tube may be detected 

 soon after it has separated from the general blastema ; 

 in this case the stomach, gullet, and intestine, have 

 assumed their proper form and position, but there is 

 no distinct cavity, and consequently no adult mucous 

 or muscular layers. Among Annelids the development 

 of the feet demonstrates the same fact. Furthermore, 

 we have observed decided contractions take place in 

 exclusively sarcodic masses, in which no reagent 

 could show the fibres, although these are present at a 

 later period. 



Thus, we see that in certain instances not only the 

 external features, but the intrinsic properties, pre- 

 exist in the tissues, and that the latter originate 

 directly in the sarcode, either by a sort of progression, 

 or by condensation, or by an aggregation of mate- 

 rials drawn from the general nutritive supply of the 

 being. 



There are already many facts in opposition to 

 Schwann's doctrine, and it is most probable that, as 

 the subject is more considered, they will increase 



* I may state here, that, in a most interesting memoir on the 

 anatomy of Medusidse, M. Agassiz, a naturalist of great repute in 

 Europe, but who nevertheless abandoned the Old World for the 

 United States, describes one of these radiates, whose nervous and 

 muscular systems are entirely cellular ; but even this exception 

 from its exaggerated character is quite beyond the range of 

 Schwann's theory. 



D 2 



