46 ILLINOIS BIOLOGICAL MONOGRAPHS [46 



tive study of the cestodes of Gasterosteus aculeatus and G. pungitius. 

 There is doubtless a large amount of such material already brought 

 together in the museums and private collections of Europe upon which 

 an investigator could work. 



Schneider's material was found for the most part in Gasterosteus 

 pungitius from Obersee near Reval, Esthonia (a province in Russia) 

 in the months of May and June. Never more than four cestodes of this 

 species were found in a single host. He also studied a single specimen 

 found by Dr. K. M. Levander in Gasterosteus pungitius. This speci- 

 men was reported by Schneider (1902:84, 86-87) as Ichthyotaenia fili- 

 collis (Rud.). For my study Dr. H. B. Ward very kindly secured one 

 of Schneider's specimens of this species, stained in carmine and mounted 

 in toto, from Dr. K. M. Levander in Helsingfors. It bears the label, 

 "Ichthyotaenia ambigua, int. Gast. pungitius 23/10 VI, 04." The 

 description which follows is based on Schneider's (1905:21-24) descrip- 

 tion and on the writer's observations on this one mounted specimen. 



Schneider's longest specimen measured as much as 35 mm. long 

 by a maximum breadth of 0.8 mm. and it possessed 17 proglottids. Of 

 these the anterior were broader than long and they were united by their 

 whole width. Proglottids well filled with eggs are longer than broad 

 and have a well rounded outline. The specimen studied by the writer 

 has about 25 proglottids. Of this number but a few at the anterior end 

 are young. These are followed by a large number of nearly mature 

 and mature proglottids and these in turn by a small number of ripe 

 proglottids. The strobilation is indistinct. The first proglottids meas- 

 ure about 0.075-0.080 mm. long by 0.200 mm. broad while the mature 

 proglottids measure about 0.180 mm, long by 0.370 mm. broad and the 

 ripe ones about 0.48-0.660 mm. long by 0.45 mm. broad. An end pro- 

 glottid tapers posteriorly and is 0.975 mm. long by 0.425 mm. broad. 

 Schneider states that the scolex is small, 0.100-0.120 mm. broad, and 

 not well set off from the neck. The suckers measure 0.055 mm. in diam- 

 eter. No fifth sucker is present. The neck is relatively broad and its 

 length is about one-fourth that of the body. In the specimen examined 

 by me the breadth of the head at the base of the suckers is 0.090 mm. 

 It is very short and not well set off from the rather broad neck. Suck- 

 ers are about 0.042 mm. in diameter over all. The first traces of seg- 

 mentation occur at a point about 1.0 mm. behind the head. This makes 

 the neck equal to about % the length of the entire body. 



It is stated by Schneider that the excretory vessels are quite wide ; 

 that the two ventral vessels which communicate in each segment with 

 the exterior through a submarginal pore measure 0.03 mm. in diameter ; 

 and that the dorsal vessels are smaller, their diameter being 0.0075 mm. 



