80 INVERTEBRATE ZOOLOGY. 



(h) A mature link. Here the eggs have formed, and filled the uterus, which 

 has branched enormonsly in order to accommodate them. The other organs, 

 except the ovidnct. have become suppressed. 



52. Cross-section of a Proglottid. This is to be prepared for the class as 

 in the case of the Sycon sponge [22], cut on the microtome and mounted. In 

 this observe: (a) The body-parenchyma, filling all the spaces between the 

 organs and leaving no coelom. The parenchyma is crossed by ntuscular Jibres 

 which in general run parallel with the body- wall, and surround the organs. 

 Upon the outside of the parenchyma there is a thin transparent cuticala. (b) 

 Two lateral excretory canals cut across. The section may show a portion of 

 a transverse canal connecting the lateral tubes, (c) The eggs which mark the 

 position of the uterus. The double contour shows the presence of a thick 

 shell. If the eggs are developed, three pairs of delicate chitinous hooks may 

 may be seen in some, appearing as parallel lines. Such forms are the '-six- 

 hooked embryoes." ready to penetrate the walls of the stomach of their first 

 host and encyst themselves in the liver. These hooks are provisional organs 

 and not the same as the definite hooks of the Scolex. 



53. TJte encysted Scolex (=Cys1icercus). This is the Taenia as it develops 

 from the egg, and encysts itself in the body of its first iiost. The cysticercus 

 of this species is found in mice and must be sought for as follows : — Open a 

 mouse by a median ventral incision and either pin it open on the table or bend 

 it gently backwards over the finger. Find the live)-, a dark red mass consist- 

 ing of several lobules, lying just beneath the .diaphragm a little on the right 

 side. Look over the surface of all the lobes for a large round whitish spot 

 shading off into the red. This spot should be nearly as large as a pencil end 

 and indicates the presence of an oval cyst the size of a pea, imbedded in the 

 liver substance. When such a cyst is found it should be carefully dissected 

 out, and opened under the lens by a small incision at about the middle. Search 

 carefully for a rounded scolex, with hooks and suckers, resembling the scolex 

 of the adult Taenia. When found, carefully remove the superfluous portion 

 of the cyst, preserve the scolex as directed in 42 a, and when thoroughly pre- 

 served, flatten slightly and stain with borax carmine as in the case of 

 hydroids [33]. 



Type VIII.— A Rotifer (especially gen. Rotifer or Brachionus). 



These are microscopic forms ftnmd in fresh water, about the size of large 

 ciliate Infiisoria and when first discovered, classified with them. They are in 

 reality minute Metazoa with development from eggs. Recently through the 



