2 The Microscope. 



Ch. acanthodes strike the soft-bodied infusorian Lagynus, and tear 

 away the sarcode in drops and dripping shreds, which the assaulting 

 animal swallowed. In view of these qualities, which are striking in 

 more senses than one, it seems rather strange that they should seek 

 the oozy depths of the ponds and the dark places where the aquatic 

 plants thrust their roots into the mud. Yet at times they are taken 

 among the rootlets of the floating Lemna ; I have even found their 

 eggs among these tangled filaments, where the parents have care- 

 lessly dropped them. The food supply is the probable secret of the 

 preference. The organic debris, the fine residual detritus of the 

 microscopic plants and animals whose life has been quenched in the 

 waters, appears to form their chief nutriment. In two instances, 

 both being with different individuals of the same large Ch. rhomboides, 

 a living diatom was swallowed. These are the only cases that I have 

 seen where any but minute particles were accepted as food. 



Although the animals are abundant in our fi'esh waters. Prof. 

 C. H. Fernald's interesting paper on Ch. lams, Ehr. , published in 

 The American Naturalist for December, 1883, is, so far as I know, 

 the only one on the subject in American print, with the exception of 

 allusions scattered through various journals where the writers usually 

 seem to doubt the correctness of the identification. This earliest dis- 

 covered European species, therefore, is the only one noticed in this 

 country so far as there is any record. In Europe the literature is 

 but little more extensive. Joblot, in 1718, evidently figures and 

 refers to one form which he calls " Poisson k la tete treflee," a fish 

 with a trefoil head, but to old Joblot almost everything aquatic and 

 microscopic was a fish. Ehrenberg, Dujardin, Schulze, Gosse, 

 Metschnikoff, Ludwig and Biitschli are the more important and 

 accessible European writers on the subject in general. 



A glance at the figures in Plates I and II will show, as has 

 already been said, that the bodies of all closely resemble each other 

 in outline. In internal structure the differences are also surprisingly 

 slight. The animal consists of a free-swimming, flexible, elongated 

 body, the anterior extremity usually enlarged to form the so-called 

 head, a slight constriction behind this part constituting the neck, the 

 central portion of the body being formed with convex lateral borders 

 and a more or less strongly arched dorsum, the degree of dorsal 

 convexity depending upon the presence or absence of an ovarian egg, 

 the region being variously appendaged and suddenly narrowed to 

 form the posterior extremity which is conspicuously bifiu'cate, the 

 furcations constituting two short, curved and flexible caudal 



