2360 Journal of Applied Microscopy 



Planarians. 



Planarians belong to the phylum Platyhelminthes, which includes the most 

 simply organized worms. The Platyhelminthes are divided into three main 

 branches. These are : (1) Tiirbellaria, (2) Ttrtnatoda, (3) Cestoda. The plana- 

 rians fall within the first of these main branches, viz., the liirbellaria. The 

 Turbellaria are usually divided by systematists into three principal groups : the 

 Folyc/adida, the Tridadida and the Rhabdocoelida. It is with representatives of 

 the last two groups, the triclads and rhabdocoeles, that we are concerned here. 

 Numerous representatives of both these groups are found very commonly in 

 fresh water over a large portion of the globe. The fauna of Michigan is espe- 

 cially rich in representatives of both these groups. 



It is the purpose of these notes to point out to teachers the importance of 

 these organisms in teaching work, and to suggest some specific uses to -which 

 they may be put. Hints regarding their collection will also be given. 



(1) Planarians found in Michigan. 



We have in Michigan a number of species of the family Pianatidce, or plan- 

 arians sensH stridii. The most common representative of the family in the 

 southern part of the state is the well known Plaiiaria macnlata. This is a small 

 worm, mottled grayish-brown in color, ranging in length from 5 mm. to 20 mm. 

 (approximately). It is roughly cigar shaped in outline and is markedly flattened 

 in the dorso-ventral direction. Besides P. macnlata several other species of the 

 genus Planaria are commonly found in the state. The genus Dendroavlum is 

 represented by at least one species. 



The forms just mentioned all belong to the group Tridadida. No systematic 

 study of the rhabdocoele fauna of the state has ever been attempted, so that only 

 an approximate statement regarding their occurrence can be made. A consid- 

 erable number of species, representing several of the families of the Rhabdoavlida, 

 have been found by the writer in the region about Ann Arbor, and there is no 

 reason to suppose that these forms are more abundant in this than in other parts 

 of the state. 



In general it may be said that there is little doubt that any teacher in the 

 state can, with very little trouble, collect in his immediate locality representatives 

 of a number of species, both of the Tridadida and the Rhabdocxlida. It should 

 be added that wherever planarians are found at all they are almost invariably 

 found in large numbers. Hundreds of specimens of Planaria may be collected 

 in a few hours after one has found a locality where they occur. 



(2) The Collection and Care of Planarians. 



The common species of triclads {Platiaria macnlata and other species of 

 Planaria) are most usually found on the under side of stones and bottom debris, 

 in not too rapidly running water. Portions of rivers and smaller streams where 

 the bottom is covered with stones from two or three inches up to a foot in diam- 

 eter will usually yield planarians in large numbers. Dendrocadnni is more usually 

 found in pools of stagnant water, as are almost most of the rhabdocoeles. 



