north of Port Rowaa the sample was largely made 

 up of Diagtomus ashlandi , Sida , and at least 4 spe- 

 cies of Cyclo ps. Off the wharf at Port Rowan 

 amongst the denser vegetation the sample was the 

 same except that no specimens of Sida^were ob- 

 tained. To the south of Port Rowan there were also 

 these same species, but with them many Diapt omus 

 oregonensis , Diaphanos oma leuchtenbergianum , and 

 Acr operu s harpae. As all the female copepods and 

 most of the cladocerans carried eggs or young, this 

 must be regarded as an important breeding ground 

 for replenishing the supply of the species mentioned 

 above. 



The second large area is Rondeau Harbor, 6 

 miles long and 2 miles wide. The channel down the 

 middle of the harbor is 13 feet deep but is quite nar- 

 row, and the broad area on either side of it is only 

 2 or 3 feet deep and is filled with all kinds of aquatic 

 vegetation. Several deep artificial ditches open into 

 the northern end of the harbor. These lead far in- 

 land and are so choked with water plants that it is 

 difficult to push a boat through them. Both the ditch- 

 es and harbor were swarming with plankton. Eight 

 copepods and 23 cladocerans besides many insect 

 larvae, especially mayfly and dragonfly nymphs 

 were found in these habitats. A surface tow taken 

 along the central channel was made up almost entire- 

 ly of the developmental stages of the copepods and 

 cladocerans found in the shallower water on either 

 side. Sida , Diaptomus oregonensis and Bos mina were 

 the most abundant, but there were also many Cerio- 

 daphnia, Simocephalu s, and Diaphanosoma, and at 

 least 5 species of C yclops and a few Epischura . As 

 the latter do not carry their eggs in external cases 

 but extrude them singly into the water.the indication 

 of breeding was found in the presence of well devel- 

 oped eggs within the oviducts of the females. 



The third large area is Sandusky Bay which is 

 15 miles long and 4 1/2 miles wide at its maximum, 

 with an average depth of less than 4 feet. The 

 shores are lined continuously with reeds, rushes and 

 other water plants. The Sandusky River runs into the 

 south side of the bay, about one -fourth the distance 

 from the inner end to the mouth. Numerous creeks 

 drain into the bay from either side. In a tow taken 

 near the mouth of the river, 9 species of copepods 

 and 10 of cladocerans were obtained; of the former, 

 6 species of Cyclops were especially abundant, with 

 the males considerably outnumbering the females. 



Diaptomus s icilis was also present in very large 

 numbers and this bay is evidently the breeding 

 ground of that species just as Long Point Bay is for 

 the species J), ashlandi . Among the cladocerans, 

 Leptodora and Bosmina were most numerous, with 

 Di aphanosoma a close third in abundance; the two 

 former were evidently breeding while the latter was 

 carrying young fully developed and ready to emerge. 



To test the importance of the creeks which empty 

 into the bay a tow was taken in one of them. Pickerel 

 Creek, about a mile above its mouth and just below 

 the highway bridge. This tow yielded 6 species of 

 copepods and 8 of cladocerans; 5 of the copepods were 

 Cyclops. Four of the cladocerans were the same as 

 those obtained in the bay and four were different; 

 only 2, Daphnia and Diaphanosoma , were abundant. 



The larger areas just enumerated and the smaller 

 ones previously mentioned are integral parts of the 

 lake itself and would naturally be expected to con- 

 tribute to the maintenance of its plankton. But there 

 are also other localities outside the lake where the 

 breeding of plankton occurs on a scale large enough 

 and of sufficient duration to produce more than a lo- 

 cal supply. These supplement the smaller and larger 

 areas already discussed and constitute a third group, 

 not as efficient as either of the others, but still con- 

 tributing their quota towards the desired result. Each 

 of the localities in this group is connected with the 

 lake by a creek, stream, or river, through which the 

 surplus of its entomostracan fauna is carried into the 

 lake. Two such localities were visited and the plank- 

 ton obtained from them verified the statements made 

 above. The first of these was Portage River at Port 

 Clinton, Ohio, where the river above its mouth widens 

 out into a sort of bay with only a thin fringe of aquatic 

 vegetation. A single vertical tow from a depth of 10 

 feet to the surface captured the following: 



Species 



Cyclops albidus 

 Cyclops leuckarti 

 Cyclops senulatus 

 Cyclops viridis 

 Diaptomus ashlandi 

 Diaptomus minutus 

 Diaptomus oregonensis 

 Diaptomus sicilis 

 Epischura lacustris 



Number captured 



9 



368 



15 



4 



157 



63 



797 



7 



45 



151 



