OF THE PROTOZOA. PSOROSPERMIA. 265 



vertebrate animals — worms, moUusks, and insects, — but have not been found 

 in Vertebrata. 



B. — PsoROSPERMiA (Plate XXII. 37-41). — This is a small group of para- 

 sitic animals, first observed by John Miiller in 1841, closely related to the 

 Gregarinida, of which, indeed, they might be included as members. Unlike 

 the Oregarince, they live upon vertebrate animals, viz. upon many species of 

 fish, about their skin, giUs, and internal organs, several together enclosed 

 within sacs. 



Leydig has more recently applied himself to the study of these minute 

 parasites, and has given the results of his observations in Miiller's Archiv for 

 1851, of which an abstract appeared in the Journ. of Mic. Science, i. p. 206, 

 which we shall here take the liberty of using, as sufficient for our pui'- 

 pose : — 



'^ The Psorospermia are microscopical corpuscles of a peculiar kind, which 

 may be generally characterized, in the full-gro^Ti condition, as rounded 

 organisms, having a sharply- defined outline, with or without a tail-like ap- 

 pendage. They are flattened and lenticular in figure, and one pole is usually 

 acuminate ; and towards this pole several internal vesicles converge in a 

 symmetrical manner. These creatures were discovered by John Miiller in 

 1841 (Miill. Archiv, 1841, p. 477). He found in a j^oung pike minute round 

 cysts in the cellular tissue of the muscles of the eye, in the substance of the 

 sclerotica, and between this and the chloroid coat. The contents of the cysts 

 was a whitish substance, which, when examined microscopically, Avas found 

 to consist of peculiar elements — the ' Psorospermia.^ [A detailed notice of 

 these observations is given in the Microscop. Journal, vol. ii. p. 123, and in 

 the Brit, and Foreign Med. Rev., January, 1842.] In the following year the 

 same observer (Miiller's Archiv, 1842, p. 193) discovered parasitic corpuscles 

 in the swimming-bladder of a Gadus CaUarias, which, although specifically 

 distinct from the Psorospermia, approached very near to the latter in their 

 organization. They resembled in general a smooth ventricose Navicula, and 

 consisted of two elongated cases apphed to each other at the cavity, and with 

 an elliptical outline and convex outer surface. They were in part free, in 

 part enclosed in masses within a tunic. Similar cysts, containing Psorosper- 

 mia, have been found by Leydig in several species of fish, and in aU parts 

 nearly of their bodies, and even in the blood contained in the heart and in 

 the peritoneal cavity. 



" Some facts, however, observed by him, connected with this subject, which 

 came under his notice in 1850, during some researches on the cartilaginous 

 fishes, served to throw a more general light upon these mysterious forms. 



" In the gaU-bladder of a Squatina Angelas there occiuTed in the bile, and 

 in large quantity, peculiar forms of various organization, but which were 

 manifestly developmental forms : — 1. Rounded vesicles, consisting of a delicate 

 membrane and a consistent fluid ; the latter was of a yellow colour, and con- 

 tained a multitude of also yellow granules. 2. Other vesicles presented, be- 

 sides these, other elements of a new kind : in the middle of the granular 

 contents were several perfectly transparent cellules ; smaU vesicles had only 

 one of these cellules, larger ones as many as six. 3. Other parent vesicles, 

 again, exhibited, besides their membrane, a granular contents and secondary 

 vesicles, containing Psorospermia, always one in each secondary vesicle. 4. 

 In the latter form, finally, the secondaiy vesicle had attained a large size, 

 and the Psorosperm floated in a spacious clear chamber, which occupied nearly 

 the whole of the parent cyst. Besides these motionless cysts, there were nu- 

 merous free Psorospermia in the bile. 



" He found, upon examination, very similar things in other fishes of the 



