149] LIFE HISTORY OF GORDIUS AND PARAGORDIUS—MA Y 29 



parasites, two from one host and one from the other, had escaped. On 

 October 19, 1914, a specimen of Orchelimum vulgare which had been collected 

 on October 15 and kept in a cage in the meantime, was placed in water. 

 Within less than five minutes six specimens of Gordius robustus escaped. 

 Similar observations were made several times after that. These observa- 

 tions show that Gordius robustus may remain for a long time in the body 

 of the host after the adult state has been reached and that it escapes only 

 under favorable conditions. 



ORGANOGENY 



On account of the large amount of material available, including speci- 

 mens of nearly all ages, it has been possible to follow out the essential 

 changes that take place from the time the larva enters the host to the time 

 the adult emerges. The following discussion is not in any sense to be the 

 final word on the organogeny of Gordius robustus, but on account of the 

 size of the field to be covered it seems best to present at this time a general 

 account of the changes involved and to leave certain particulars for further 

 study by means of special methods. 



Metamorphosis 



The changes that take place soon after the larva has entered its host, 

 as development is initiated, hardly justify the name of metamorphosis. 

 There is no encystment, the larva remaining active even a short time 

 after development has begun. The evidence for this has already been 

 given in the discussion of the infection experiments. Growth begins 

 at about the same time in all of the tissues of the body and parts of the 

 proboscis (Figs. 9, 11, 15, 50-53). Development in the proboscis is at 

 first slower than in the body, but later the difference disappears and it is 

 impossible to locate the division between body and proboscis except from 

 the location of the partition that exists between the two in the larva 

 (compare Figs. 15 and 67). The parts of the proboscis that do not enter 

 into later development are the cuticula bearing the hooks and stylets with 

 the underlying hypoderm, the muscles, and the column of cells connecting 

 the stylets with the partition between body and proboscis (Figs. 57, 67). 

 The cells found in the larva at the anterior end of the intestine (Fig. 20), 

 increase very rapidly in size at first (Figs. 11, and 15, ) but later are fre- 

 quently found to have disintegrated (Figs. 67, 68, 73) and are probably to 

 be regarded as a special organ of the early developmental stages and 

 possibly also of the larva. 



Derivation of tissues 



Most of the tissues are already outlined in the larva and merely undergo 

 further development in the parasitic stage. 



Ectodermal derivatives. The derivatives of the ectoderm of the 

 embryo are the cuticula, hypoderm and nervous system. 



The larval cuticula is retained. 



