CESTODE AND NEMATODE PARASITES. 85 



slight lateral swelling, so that this end is almost moniliform. The eggs are ahout 

 0*07 millim. in length. 



In the centre of each of the last half dozen proglot tides is a large clear place. 

 This may possibly be the remains of the genital atrium, and if it is so, this is median. 



Tetrarhynchus herdmani is characterised by having a small head with well- 

 developed bothridia, short muscular proboscis sheaths, one-tenth to one-twelfth the 

 length of head, teeth on proboscis, uniform in spiral lines, O'Ol millim. in length, 

 well-developed collar, 60 to 100 proglottides, most with parallel sides. 



Habitat : Stomach of Trygon walga and Rhynchdbabus djeddensis, MULL, and 

 HENLE. 



Tetrarhynchus macrocephalus, n. sp. Plate VI., figs. 110, 111 and 112. 



At least six different species of Tetrarhynchus are found in the intestine of Trygon 

 walga. This species is a short, stout, thick-set form, with large bothridia or lappets, 

 which, however, when the proboscides are extended, are far less conspicuous than 

 when they are retracted (Plate VI., fig. 110). 



The total body length averages 7 millims. or 8 millims., and the body is stiff and 

 straight. The relative length of the different parts of the body in one specimen, 

 whose total length was 8 millims., was 3 millims. for the part of the head traversed 

 by the coiling ducts of the proboscis sheath, 3 millims. for the part of the head which 

 contains the muscular proboscis sheath, and 2 millims. for the rest of the body. The 

 second portion, that which contains the muscular sheath, is the thickest, and its walls 

 are smooth ; the anterior half of the head is wrinkled. 



The four proboscides were in some specimens extended, but not fully ; they attained 

 a length of some 2 millims. Each bears a longitudinal double row of minute, almost 

 straight spines, diverging from one another (Plate VI. , fig. Ill), the whole producing 

 the effect of a stitch known, I believe, to housewives as "herring-boning." This lies 

 the whole length of the proboscis. There are also very numerous sharply hooked 

 spines, which lie in transverse rows some hundred or more in number. Each of these 

 rows consists of some ten or twelve hooks, grading in size from the largest, which is 

 just opposite the " herring-boning." to the smallest, which flank the " herring- 

 boning." 



When the whole is retracted it passes first into the very coiled ducts of the 

 muscular sheaths, which are very apparent in the specimen. 



The strobila is smaller than either half of the head ; the piece immediately 

 succeeding the head is anteriorly concave, and receives into its concavity the convex 

 end of the head (Plate VI, fig. 110). It soon begins to "segment," and the 

 proglottides grow rapidly. They are few in number, and the most posterior, which 

 is about the tenth or twelfth, is almost as large as all the others put together. It 

 shows clearly the exit of the water vascular system. The specimens were probably 

 young ones. 



