10 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



the peripheral portion of the fibre has a homogeneous appearance (Plate 1, 

 Fig. 3). In some cases, however, the entire fibre shows a coarsel}' granu- 

 lar condition (Fig. 2). In cross section the large fibres show a periph- 

 eral contractile portion and a central colorless core (Plate 1, Fig. 6), as 

 described in the case of the longitudinal muscle fibres of the body 

 wall. Many of the dorso-ventral muscle fibres lie along the inner mar- 

 gin of the peripheral granular parenchyma (Plate 2, Fig. 25, mu'.)', and 

 they frequently occur in pairs, one on either side of the body. 



Very conspicuous in the posterior portion of the trunk and in the 

 appendix are the long longitudinal parenchyme muscle fibres. They 

 constitute the retractors of the appendix, either passing between the pa- 

 renchyme cells or through their walls (Plate 2, Fig. 25, )nu. rtr.). In 

 cross section they give at first glance the impression of nuclei lying in the 

 network. I could find no nuclei in these fibres- 

 Mace ('82) describes the parenchyme muscle fibres of Distoma [Fasci- 

 ola] hepatica as consisting of two parts,' — a very refractive, hyaline, 

 cylindrical fibre of considerable length, and a small protoplasmic mass en- 

 closing a nucleus and lying on the side of the fibre near its middle. He 

 regards the cellular body as the remains of the primitive cell, which 

 decreases in size as the fibre grows and very probably disappears 

 altogether. 



Stafford ('96) finds that the myoblasts of the dorso-ventral muscle 

 fibres of Aspidogaster cling to the sides of the fibres, there being a single 

 myoblast to each fibre. The surface of the fibres shows a longitudinal 

 fibrillar structure, and in section the fibres appear as small deeply stained 

 rings filled with a less deeply stained substance. He says nothing in 

 regard to the possible disappearance of the myoblasts and evidently 

 regards the conditions described as permanent. 



Poirier ('85) finds parenchyme muscle fibres with a centrally situated 

 nucleus, but believes that the nucleus disappears. 



Kerbert ('81) also states that the spindle-shaped parenchyme muscle 

 fibres of Distomum westermanni show a distinct oval nucleus, which is 

 apparently centrally situated, though he does not so state. 



Whether or not the nuclei observed in the dorso-ventral muscle fibres 

 of Hemiurus crenatus ultimately disappear, I am not prepared to say. 

 They are certainly present in many apparently functional fibres of mature 

 worms. 



