48 



were, (fig. 14, 15). In the male, around the head, this membrane was 

 thrown into puckers, as represented in fig. 1 4 ; immediately below 

 this, on one side, it formed a semicircular fold, and then became pa- 

 rallel to the body of the worm throughout its whole course, until it 

 came to the tail, where again it was slightly puckered, (fig. 15). These 

 folds were more remarkable in the female than in the male, and the 

 only parts of the worm in immediate contact with this membranous 

 sheath were the extremities of the head and tail. Near the tail in the 

 male two curved dark bodies were observed, like those described in the 

 Strongylus convolutus, and immediately above them the intestine was 

 slightly enlarged, (fig. 15, a). In the female the ovaria were very long 

 and full of ova, like those of the other species, but the external open- 

 ing of the uterus was seen on the side of the body, near the end, and 

 at this point two small hooks were observed, (fig. 16, b). The intes- 

 tine proceeded a little farther on than the uterus, and terminated 

 where the tail came in contact with the sheath. The manifest differ- 

 ences between this Entozoon and any of the others previously de- 

 scribed, alone warrant me in making this a distinct species : and the 

 most striking, and at the same time most constant character, being 

 the investing membrane or sheath, I have given it the name of inva- 

 ginatus at the suggestion of my friend Dr. Willis, in consequence of 

 this peculiarity.* All the authors who have described the genus 

 Strongylus, call the membranous investment at the tail both of the 

 male and female, a bursa or sheath for the genital organs ; some of 

 them, as Kuhn, describe an intromittent organ ; but in these four spe- 

 cies I have not seen one protruded, but my friend Mr. Busk has no- 

 ticed it in a specimen of Strongylus minor. 



I cannot conclude this paper without alluding to some curious facts 

 which present themselves for our consideration. Entozoa, from the 

 time of their first discovery to the present day, have exhibited more 

 astonishing and wonderful phenomena than any other tribe of anima- 

 ted beings ; and perhaps throughout the whole kingdom of Nature no 

 class has been so frequently the subject of opposite opinions, and on 

 the matter of their generation we are now nearly as much in the dark 

 as ever. We have, nevertheless, in the specimens before us, the start- 

 ling truth of one and the same species of Entozoon living in directly 

 opposite media, viz., in blood and in air ; for it has been stated that 

 the Strongylus injlexus was found in the bronchial tubes, in the prin- 



* By means of a higher power than was used hy me, Mr. Busk has found that the 

 sheath may even he seen around the minute animal whilst in ovo. 



