INVERTEBRATE ZOOLOGY. 77 



These organs may now be searched. Place them one at a time in the small 

 glass dissecting pans on the stage of the dissecting microscope, open them 

 with the scissors, pinning them out when necessarj'. The entire alimentarj' 

 canal should be opened and its contents w^ashed out, after which the canal 

 itself may be removed. Each organ has its own separate species of Trema- 

 tode. each of which have their peculiarities of investigation, and may be sep- 

 arately treated. Any one of these will do for study alive, but the one from 

 tlie lung may be taken as the type, and is the only one to be mounted. 



45. Study of living Trematodes. (From frog.) 



45. 3,. Lung form. Study this at first superficially in a watch crystal 

 and search for the two sucking discs characteristic of the genus. Then flat- 

 ten it by compression (it will i)r()bably bear treatment between two slides, and 

 perhaps some pressure added to this) and observe hy transmitted light, first 

 with the simple lens and then Avith the low power of the compound micro- 

 scope. The most conspicuous organ is the uterus, filled with eggs. By a lit- 

 tle added pressure the eggs may be made to escape like a fine dust from the 

 genital opening. Locate this and examine eggs ^vith the high power. The 

 anatomy in general is similar to that of Turbellaria (41]. 



45. ^- The form from the (dimentarij cdnal. This is a very small oval 

 worm scarcely S""" in length. It is to be placed on a slide in a drop of water, 

 covered by a cover glass and studied with transmitted light. It is very satis- 

 factory to studj' on accoTint of its .small size and transparency. |cf. 41.] 



45. c. Tlw form from tlw hUuhh'r. This is opacpie and cylindrical and 

 should be studied only in a watch crystal of water, attached if possible in its 

 natural attitude to a piece of the bladder-wall. Its ventral sucker is enor- 

 mous, projecting and cup-shaped, and is used for attachment. The portion 

 of the bod}^ anterior to this is verj^ extensile and used as a tactile organ. 

 Comjiare and homologize the body regions and suckers of this animal with 

 those of the other species. 



46. 7b mount (I Trematode use the lung-form, fixing and staining as di- 

 rected in 42. For rapid work, the use of weak borax-carmine is recommended, 

 followed by the acid alcohol treatment. In this, as in most small Distoma, the 

 testes are not dendritic, but are in the form of compact, rounded masses, 

 which stain deeply, and which, with the similar shaped ovary, form three 

 conspicuous masses jiosterior to the ventral sucker. 



47. Larval Stages (^Asexual generations). Trematodes exhibit a com- 

 l)licated alternation of generations, the other forms being parasites of aquatic 



