24 Mindeskrift for J. Steenstrup. XXV. 



are taking place within the egg during its stay in the mucous membrane of the rat's 

 stomach and its passing through the intestine canal; in this way, to be sure, it has 

 reached a stage of development, which eggs extracted from the uterus have not yet 

 obtained. The not fully developed eggs thus are not hatched in the intestine of the 

 cockroach but passed with the excrements without change. 



The opening of the ripe egg takes place in the foUowing way: 



The thicker part of the shell at the poles actually consists of two layers, When 

 passed into the intestine of the cockroach these two layers probably influenced by the 

 secretion (Text fig. 2) begin to diverge, forming a cavity between them. The con- 

 nection with the rest of the shell is then loosened, the outer lamelle falls off 

 first, after which the inner one is broken, perhaps influenced by some pressure 

 from the foetus. In the fig. the two lamellæ at one of the poles are observed 

 to diverge from each other, at the other pole the outer lamella is gone, the inner one 

 is broken, the hind part of the young one forcing its way through the hole thus 

 made. At the same time the inner lamella has loosened itself from the rest of the 

 egg, remaining only as a sort of collar which will soon fall off. The emptied egg now 

 appears as a ring, consisting of the middle part of the shell, devoid of the thickened 

 polar fields. To a cursory view these empty eggs will now be found somewhat similar 

 to the eggs of Trichocephalus, flattened at the poles, on a more thorough examination, 

 however, no mistake is possible. 



The larva when freed from the egg has the shape of a long comma; presenting 

 the greatest width in the front part and tapering evenly towards the hind part; the tip 

 of the tail is rounded. On fresh preparations the larva shows no interior differentiation; 

 it is covered with a rather thin cuticula, somewhat thicker in front. Its length is 

 about 250 n, its maximal width 13 [i. 



Apparently the period in which the larva may be found in the chylus-intestine of 

 the cockroach is but of very short duration; even two days after the feeding they are 

 gone, as well as the eggs and the empty shells. It has not yet been discovered 

 where the larva goes to, on leaving the chylus-intestine; most probably it will make 

 its way into the intestinal wall, although it has not been found there on fresh prepar- 

 ations. A rather long time is passed after the feeding until it can be found in the mus- 

 culature (about 20 days), for the present it must be unexplained where it resides till then. 



After having entered the muscles of the cockroach the larva encysts itself, being 

 then coiled-up trichina-like. The capsule, however, in the Spiroptera-larva generally 

 is but little prominent, — as distinct from those known from the trichina. Most 

 frequently no capsule at all will be observed at first sight; only the larva will be 

 seen among the muscular fibres, coiled-up in a most graceful and regular spiral. As 

 a rule the tail is placed in the centre, the head at the outside. 



