CONTAGIOUS DISEASES OF DOMESTICATED ANIMALS. 115 



tains ouly the vitellns, lu the water coutaiued in crystallizing disbe.s, 

 small enough to be i^laced on the stage of a microscope, we have studied 

 day by day the formation of the embryo during the month of July of 

 this year, when the temi)erature maintained an averageof 25oO. (77° F.). 

 We have determined that in presence of these conditions twenty-eight 

 to thirty days s-uffice for the development of the embryo and its escape 

 from the shell. 



The embryos or larv;^ live in the water, where they swim about in a 

 serpentine manner like the anguilluhe (vinegar eels, «S:c.). At a tem- 

 perature of 20° or 25° C. (6S°-77° F.) we have been unable to keep them 

 alive for more than eight or ten days, whilst at a lower temperature 

 they lived for many months, almost a year. During this time they 

 molt, the tail becoming less elongated, and assuming the form of a 

 short cone (Plate II, Fig. 10). When the hatching has been delayed 

 from insufficient warmth, and the embryo finally escapes from the egg, 

 it leaves within the shell an envelope. This fact seems to prove that 

 the molt, which takes place normally one or two days after birth, occurs 

 in the egg itself when birth is retarded. In the experiment-glasses larvae 

 with short tails were often seen moving among those with long tails. 

 The former were simply older than the latter. 



The following questions now arise: Does the larva molt a second 

 time before assuming the adult form, and what are the ways and means 

 employed by it to reach the only place where adult and paired syn 

 games are found — the trachea of birds? 



Some species of Sclerostomata presents a nymphal phase, during 

 which the young parasite is provided with an almost complete buccal 

 armature, and lives, rolled up and encysted beneath the mucous mem- 

 brane to which it attaches itself in its adult state. Repeated investi- 

 gations have failed to reveal anything analogous in the syngame of the 

 pheasants. We have every reason to believe that the nymphal stage, 

 no doubt very short and active, is passed in the air-sacs and pulmonary 

 broiu;hi, which, as is well known, intercommunicate very largely in 

 birds, and which the larv;e may readily reach by traversing the intes- 

 tinal or oesophageal tunics after escaping from the ingested eggs. We 

 also believe that the parasites very soon after reach the trachea, to be- 

 come adult, pair, and attach themselves. The following are the facts 

 upon which this opinion is based : 



1. The larva' of Syngamus, according to our observations, do not 

 develop well, nor will they leave the egg and become vigorous except- 

 ing in a moist and warm medium, approaching the conditions ottered 

 by the interior of a bird's body. 



2. In a young i)heasant, dead from the gapes, we found in the mucus 

 obtained by scrai»ing the lining membrane of the (esophagus, a large 

 number of eggs of syngames with the shell opened and abandoned by 

 the embryo. We have preparations to demonstrate this fact. 



■J. In the serous ttuids which lubricate the walls of the air-sacs, nu)re 



