936 SUMMARY OF CURRENT RESEARCHES RELATING TO 



The vacuolated condition seen in the protoplasm of various Protozoa 

 may, perhaps, indicate the starting-point of the differentiation of an intra- 

 cellular network, or, in other words, the differentiation of the cell into 

 firmer and less dense portions, the former of which takes on the form of a 

 network ; the highly contractile fibril of Vorticella shows no trace of the 

 presence of fibrils, and appears to be simply undifferentiated protoplasm. 



Of the Coelenterata Hydra was found to have a network in the body of 

 the ectoderm cells, but this was not continued into the " muscular process "; 

 Aurelia has striped muscles in which the distinct transversa striation is 

 due to the presence of a network which is similar in all respects to the 

 network described by Eetzius and Melland in striped muscle ; in Actinia 

 the muscle showed no trace of any intracellular network or of any 

 fibrillation. Here, then, as with the Echinodermata, in which there is no 

 trace of a network, the author agrees with Dr. Hamann. 



Among worms, the leech and the earthworm were examined ; in the 

 former the muscle-fibres are very peculiar, consisting of an outer clear 

 portion and a central granular part ; no distinct fibrils could be detected. 

 In the earthworm the muscle is found to contain large elongated cells 

 with longitudinal lines, which under a 1/10 immersion objective present a 

 dotted appearance ; the dots, however, are quite irregular, and do not extend 

 into the body of the cell. 



In the Mollusca, the limpet was found to have the network of striped 

 muscle in its muscle, and the same was found in the muscle of the snail's 

 odontophore, and in the adductor muscle of Pecten, which differs from 

 most of its class by using that muscle to propel itself through the water. 

 Striped muscle was found in various Arthropods, and in the muscular bands 

 of Salpa. 



As to the Vertebrata, it is to be noted that the striation of cardiac 

 muscle appears to be due to an intracellular network similar to that of 

 ordinary striped muscle. 



If we resume these facts, we find that striped muscle is ordinarily 

 associated with energetic animals or movements ; the presence of such in 

 some sluggish animals, such as certain insects, may be supposed to be due 

 to inheritance. We find that (1) an intracellular network of a definite 

 character is present in the fibre of striped muscle throughout the animal 

 kingdom. (2) This network is developed where rapid and frequent move- 

 ments have to be performed. (3) The striped muscle-fibre consists of 

 sarcolemma, network, and sarcous substance ; and, so far as at present 

 determined, there is no other structure present in the fibre (except muscle- 

 corpuscles and nerve-endings). With regard to the mode of action of striped 

 muscular fibre, Mr. Marshall is of opinion that its construction is due to 

 the active contraction of the longitudinal bars of the network, and that the 

 transverse networks are probably passively elastic, and cause by their 

 rebound relaxation of the fibre. It is possible that the transverse networks 

 and the muscle-corpuscles with which they are said to be continuous, 

 furnish paths by which the nervous impulse is conveyed from the nerve- 

 ending to the longitudinal bars. As to the contraction of unstriped 

 muscle, it is probably due to the active contraction of its longitudinal 

 fibrils, when such, as in vertebrate muscle, are present; when they are 

 absent the contraction must be referred to the whole protoplasm of the cell, 

 for there is no special part differentiated to perform the function. 



The author is aware of two objections to his suggested explanation ; 

 the first affects the supposed difference between the longitudinal and 

 transverse bars of the same network ; but it is possible that the latter are 

 really, as Eetzius thinks, direct processes of the muscle-corpuscles. The 



