THE LEECHES OF MINNESOTA 21 



taining ova, spermatozoa and some albuminous material) by sper- 

 matozoa introduced into the uterus directly thru the external open- 

 ing. 



Some leeches, like Nephelis, lay a few eggs at a time in small 

 tough capsules that the leech attaches to the submergd parts of 

 water plants, stones &c. Others, like Hcemopis, enclose a few eggs 

 in egg-shapt capsules or coccoons that may be half an inch or more 

 in length. These coccoons are deposited in masses of decaying 

 vegetation, such as the submergd portions of muskrat houses and 

 the accumulation of ded roots, leaves and water plants near the 

 shore or on the bottom of the lakes. Others, like Placobdella 

 rugosa, carry the eggs and young attacht to the ventral surface of 

 the body until the young are able to move about actively and find a 

 host for a meal of blood. In these cases the eggs are laid in small 

 spherical clusters, each mass surrounded by a delicate membrane of 

 a mucous-like substance secreted by skin glands. A number of 

 such groups of eggs are somewhat loosely held together and are 

 attacht to the ventral surface of the parent by a substance similar 

 to the membrane around each spherical mass of eggs. When thus 

 burdend with eggs or young the leech does not travel about very 

 much but stays in some protected place and by undulatory move- 

 ments of the body keeps the collection of eggs or young well aerated 

 until the young are able to shift for themselves. If the egg masses 

 become dislodgd the parent will make efforts to collect them and 

 again attach them to her body. Several Placobdella parasiticas with 

 young in various stages of development are shown in Plate A. 



The development and anatomy of the leeches in general and 

 certain special structures of two or three annulata that appear to be 

 on the border-line between the leeches and other groups of annulata 

 indicate that the leeches are more closely related to the group of 

 earthworms than to any other group of the annulata. 



