[141] NOTES ON ENTOZOA OF MARINE FISHES. 859 



with that of the other at the point of contact. The inner cavity, as 

 shown in these sections, is very small, being, in fact, but little more than 

 twice the diameter of the retractor muscle which it contains. The cav- 

 ity instead of being central is really at one side. In each case it is at a 

 side which adjoins one of the other bulbs, but so disposed that each of 

 the four cavities lies at one of the partitions which separate the bulbs 

 from each other. The thick wall of a bulb is composed of several, in 

 some places as many as six or seven, alternating layers of muscular 

 fibers, whose cut ends show that they run in alternating spiral di- 

 rections from one end of the bulb to the other. The layers are rather 

 thick, in some cases at least being equal to the diameters of a dozen 

 fibers. The retractor muscle, which is itself made up of a number of 

 parallel fibers, is usually oblong or elliptical in section, but sometimes 

 nearly circular. 



The following maximum dimensions show the proportions of these 

 parts : 



mm. 



Diameter of the bulb 0.158 



Diameter of inner cavity of bulb 0.039 



Diameter of retractor muscle 0. 019 



Thickness of muscular wall of bulb 0. Ill 



Sections made near the anterior end of the head reveal a very dense 

 tissue throughout. They are divided into quadrants by two bands of 

 transverse fibers which bisect each other at the center. Toward the 

 outer edge these transverse fibers become indistinct amidst the denser 

 tissue of the outer part of the head. In each of the quadrants thus 

 formed one of the proboscis sheaths lies. The walls of the sheaths are 

 made up for the most part of fine circular fibers. In some of the sec- 

 tions the sheath, the proboscis, and the retractor muscle of the latter 

 could be plainly seen. The walls of the proboscides are thicker than 

 those of the sheaths, and like them are composed of circular fibers. 

 The sheaths are accompanied on all sides, except that which is turned 

 toward the central axis of the scolex, with strong longitudinal muscular 

 fibers. 



Near each sheath on the inner side, or rather between each sheath 

 and the point at which the transverse bands of fibers cross, there is an 

 irregular circular cluster of granules. They indicate the presence of 

 longitudinal vessels, of whose exact nature I am not certain. They are 

 stained deeply by the carmine, and are quite different in appearance 

 from the cut ends of longitudinal muscle fibers. Towards the base of 

 the sheaths these vessels have a distinct limiting membrane. Their 

 cross-sections, in the mean time, become somewhat circular. They now 

 lie close to the proboscis-sheaths. They follow the proboscis-sheaths to 

 the anterior ends of the bulbs, where they disappear. I am inclined to 

 regard them as nervous vessels. 



In the sections behind the bulbs the tissues appear rather spongy, 

 with longitudinal fibers interspersed. Towards the circumference there 



