283] NORTH AMERICAN MONOSTOMES 65 



pickt und gelangen in den Vogeldarm, wo die Embryonem ausschliipfen. 

 Mit den Excrementen werden letztere ins Freie befordert, wo sie, sofern 

 die Moglichkeit zur Infektion vorhanden ist, direkt in die Federfollikel 

 der jungen Vogel einwandern. Im andern Fall bilden sich Dauercysten, 

 die nach langerer Entwicklungsruhe such auflosen und den eingeschlos- 

 senen Organismus frei lassen, so dass er ebenfalls in die Federfollikel ein- 

 wandern kann." This summary of Jegen is supported by experimental 

 evidence gained by incubation of the eggs in a portion of the intestine of 

 an infected bird as well as by numerous attempts to incubate the eggs 

 which had not passed through the intestine of the host altho he says these 

 gave negative results. The "Dauercysten" he found in excrement of infec- 

 ted birds, which was dried by exposure to air, and at other times in the 

 nest and on the feathers of young sparrows. 



The outline of Jegen gives essentially a direct development which 

 omits the parthenogenetic stages observed in all cases where the life 

 history of digenetic trematodes is known. Observations of the writer 

 support the view of Tyzzer that a miracidium is present in the mature egg 

 in the uterine egg sac. The fully developed miracidium shows well devel- 

 oped germ balls. This is in direct contrast to the findings of Jegen who 

 says that the embryo contains two well developed germ balls with numer- 

 ous others which disappear later in course of development. Jegen found 

 that the eggs would develop only in the intestine of the host and when fed 

 to uninfected birds empty egg shells and embryos were found on the second 

 and third day. He neither states nor demonstrates that these experimental 

 birds became infected with the adult parasites. 



The work of Jegen dealing with the life history of Collyriclum is full 

 of gaps. • The life history as given is bridged over by supposition. The 

 infection of the sparrows by feeding of eggs is not demonstrated, only 

 the presence of embryos which may well be miracidia. Jegen does not 

 demonstrate beyond doubt that these cause the formation of the cysts in 

 the sparrow. The "Dauercysten" which he says infect directly the host 

 based on his experiment of the dried excrement certainly serve to protect 

 the parasite from dessication until it can reach the intermediate host; 

 nothing indicates whether this be a miracidium or another infective stage; 

 and the periodicity of occurrence of the adult parasite in correlation with 

 a rainy season tends to show that the former is the correct interpretation. 



The work of Jegen is apparently a misinterpretation of the life history 

 and leaves much to be done in order to demonstrate the facts. The only 

 clear contribution of this author to the life history of this form lies in the 

 discovery of the "Dauercysten" which he apparently misinterpreted. 

 Many more extensive and careful experiments must be carried out in order 

 to demonstrate conclusively the complete life history of this form. 



