GASTRODES PARASITICUM KORDTNKKF, 77 



ribs are not represented altogether; the condition of the tentacular 

 apparatus (/), however, shows no difference from that in the preceding 

 stage. 



Next in the individuals of the stage represented in fig. 4, the 

 diameter of the body measures some 0.5 mm.; the gastro-vascular system 

 is in the form of a connected pair of cavities, each of which is laterally 

 divided into four peripheral pouches representing the meridional canals 

 {m. c). The opening on the ventral surface is scarcely compressed; the 

 tentacular apparatus (i) is indicated merely by a thickening of epidermis 

 appearing sickle-shaped in the dorsi- ventral view. This represents the 

 stage that has been described and figured by Korotneff and Heider, 

 both of whom had apparently observed no examples of more advanced 

 stages. 



In individuals still smaller in size (0.2-0.3 nim. in diameter; figs. 

 5, 6), the rudiments of the tentacular apparatus (/) are defined only 

 indistinctly, the gastro-vascular cavity exhibits an appearance of a 

 single roomy central cavity, which may be divided peripherally into 

 four subequal parts in relatively large examples (fig. 5)- ^^ ^gs. 7-10 

 the views of the animals stained with borax-carmine are represented. 

 The individual shown in fig. 7 is in about the same developmental stage 

 as the specimen in fig. 6, and the gastro-vascular cavity is roundish 

 in form, although its outline is not represented clearly in the figure. 

 No rudiments of the tentacular apparatus can be recognized as yet. Fig. 

 16 illustrates a vertical median section of this stage. 



In stages still earlier than the above the external form differs 

 considerably from that of the older stages. Thus, in the stage represented 

 in fig. 8 the body is much less flattened than in the preceding stages 

 and is approximately hemispherical and somewhat concave on the 

 ventral side. Next in fig. 9 the body is subcylindrical, much higher 

 than broad, bluntly pointed at one end and slightly concave at the 

 other; the breadth of the body measures about 0.08 mm, and the 

 height about 0.12 mm. Unfortunately, I could obtain no sections of such 

 early stages, but so far as could be witnessed by superficial observations, 

 the animal had developed no opening at the centre of the ventral surface 

 as yet. The last mentioned stage seems to be nearly the earliest one 

 that can be observed in the mantle of the host. But I was fortunate 

 enough to secure a younger individual (fig. 10) killed apparently while 

 trying to bore into the body of the host, with one half of its cylindrical 

 body imbedded in the test of the host, and the other half lying freely 



