427 



muscles; they consist of several cell columns, and though in 

 the adult they are not to be distinguished from the abdominal 

 muscles, yet in their embryonic state the differences are 

 obvious. 



The individual muscles which constitute the leg muscles, 

 antennal muscles, and the muscles of the mouth appendages 

 and of the ovipositor, are similar to the longitudinal 

 abdominals in structure ; but their simplicity is a secondary 

 condition — a whole group of them is morphologically the 

 equivalent of a single pharyngeal dilator. J 



The contractile substance of all these muscles has assumed 

 the same type of appearance, viz., striations in the form of 

 double spirals. In the pharyngeal dilators a certain amount 

 of cytoplasm remains non-contractile ; this contains the nuclei, 

 sometimes as many as 15 in number, and is frequently in the 

 form of a bulging mass on the side of the contractile 

 syncytium (fig. 124). In the other muscles the nuclei are 

 arranged in a row along the middle of the fibre. 



In their development the fibrillae are first formed ; each 

 of these then breaks up into successive "striations" as above 

 described, adjacent striations disposing themselves in the form 

 of a double spiral. The Krause's membranes are likewise 

 fibrillar structures; but it is not impossible that adjacent 

 Krause's membranes unite, though I have never been able to 

 see clear instances of this fusion. It is interesting to note, 

 however, that artificial breaks generally occur right across a 

 fibre along a series of adjacent Krwiise' s membranes, indi- 

 cating that there is at least some coherence between adjacent 

 fibrillae. 



In all cases, the outer cell walls of the syncytium remain 

 as the sarcolemma of the muscle. 



But the most interesting of all the muscles are the great 

 vertical and horizontal thoracic muscles, and nothing like 

 them seems to occur elsewhere among contractile tissues; they'^ 

 serve, indeed, as a remarkable instance of a great number of 

 cells co-operating in different ways to form one highly efficient ^- 

 organ. The original syncytial mass forms what corresponds^ 

 to the sarcoplasm of other muscles, while the contracting fibres 

 (sarcostyles), devoid, as they are, of fibrillae, correspond to 

 the fibrillae of intracellular structures. It is interesting to 

 note that the striations of adjacent sarcostyles are likewise 

 disposed in the form of double spirals in the "muscle" as a 

 whole, and it is particularly suggestive to note, that in this 

 case, where the analogy is otherwise so extraordinarily close, 

 no connection exists between adjacent "Krause's membranes." 

 Even the sarcolemma of other muscles is represented, and it 



