EVIDENCE THAT IRONUS IS CARNIVOROUS 201 



5. Ironus ignavus Bastian. TiTi TI [76 ~Ti iTT 2 ' 7 "' The pharyngeal 



onchi are tissue tearers. The three onchi of Ironus ignavus are of unequal form 

 and size. At first glance they appear equal, but even when the onchi are drawn 

 in and the head viewed in profile it is sometimes possible to see that the dorsal 

 onchus differs from the other two in being duplex. When the onchi are exserted 

 the expansion necessary to this operation throws the two apices of the dorsal 

 onchus wide apart, and they can then with ease be brought separately into 

 focus. A front view of the head also emphasizes this double structure of the 

 dorsal onchus. Either half of this onchus when seen in profile seems to be of 

 almost exactly the same size and contour as one of the submedian onchi. The 

 action of the onchi in Ironus is like that in some species of Diplogaster, of most 

 species of Axonolaimus and of one or two other marine genera, and is the exact 

 reverse of that of the onchi of Enoplus and its relatives. The outward action 

 of the onchi in Ironus is adapted to tearing open the tissues upon which it feeds, 

 the fluid and semi-fluid portions of which are then imbibed. In harmony 

 with this is the liquid or finely divided character of the contents of the intestine 

 in Ironus. Enoplidae, on the other hand, bolt their food. The movements 

 of the onchi do not appear to be so quick as those of the onchi of Diplogaster. 

 The outward throw and return occupied about one-quarter second in a specimen 

 which though stained intra vitam with neutral red, yet appeared to be as active 

 as the average living specimen. 



Characteristic Intestinal Crystals. The doubly refractive crystals found in 

 the intestinal cells of Ironus are different from those found in certain Rhabdites, to 

 which I have given the name Rhabditin. The doubly refractive crystals of Ironus 

 are not spherical, on the contrary are distinctly angular in contour and have a 

 definite polyhedral form. These doubly refractive bodies are absent from the 

 anterior part of the intestine for a distance about equalling half the length of the 

 neck, indicating a different physiological condition here. Some of the intestinal 

 cells are very distinctly specialized. (See Fig. 5.) 



Carnivorous. The following are strong reasons for regarding Ironus as car- 

 nivorous; (1) Recognizable plant remains are rarely if ever found in the intestine. 

 (2) Ironus abounds in places where there is little plant food of any kind, but where 

 animal food is plentiful. (3) The peculiar mouth parts can hardly be ex- 

 plained in any other way than by supposing them to be special organs for rip- 

 ping open tissues of the food, and the only filter-bed plants that could furnish 

 adequate food for Ironus are entirely too small to be operated upon by these 

 mouth parts. 



A very noticeable feature in the development of the eggs of Ironus ignavus 

 is the appearance in the ripening ova of numerous protoplasmic structures which 

 stain rather strongly in acid carmine. Toward a dozen of these structures 

 may be seen in the full grown ovum when about to turn and pass into the uterus. 

 The younger ovum immediately following it also shows these same structures, 

 more closely packed together, but of about the same size. After the egg has 

 passed into the uterus these bodies sometimes completely disappear. 



Newly Discovered Organs. Among the numerous new facts here brought to 

 light in connection with Ironus none appear more interesting than the pro- 

 nounced dorso-ventral differentiation of the intestine. In both ignavus and 

 longicaudatus this differentiation is pronounced, especially in the latter, where 

 from one end of the intestine to the other the difference in structure between the 

 dorsal and ventral sides is very striking. In ignavus the same quality of dif- 



