190 LOWER INVERTEBRATES. 



to a sea^weed, with the anterior end of the body raised as if in search of a new sup- 

 port. The genera occurring in America have hardly been studied yet. Let us hope 

 that this gap in our knowledge of the American fauna will soon be filled. 



The land planarians were first discovered by the celebrated Danish zoologist, Otto 

 Friederich Mtlller, in moist earth under stones. A very few species have been found 

 in Europe, but none as yet, to my knowledge, in the United States ; but in South 

 America Charles Darwin found numerous species inhabiting the moist earth of the 

 primitive forests, where they attain a truly tropical luxuriance of size and color. 



Okdee II. — RHABDOCCELA. 



The Rhabdoccela are planarians built on a smaller scale and simpler pattern. Some 

 of them are sure to be found together with the true planarians in our ditches. 

 There are two forms which I have found most abundantly in New England. The 

 larger one, which I take to be identical with Mesostomuin ehrenbergi, is 

 a third of an inch or more long. It is whitish and translucent, and has 

 a broad, dark streak in the middle of the body, an effect produced by 

 the dark contents of the stomach, which the Mesostomum always keeps 

 well filled as long as it can secure food. If one of these worms be kept 

 in filtered or distilled water it finds nothing to eat, and the stomach 

 is gradually emptied, and the worm appears of the same translucent 

 white tliroughout. This species is admirably adapted to anatomical in- 

 ■\-estigation because its transparency reveals all its internal organs. The 

 two eye-specks are very conspicuous in front; the mouth is near the 

 middle of the ventral surface, and is armed with a long proboscis; 

 Fig. 167.— ii/esos- the stomach, as in all the Rhabdoccela, is a simple wide sac without 



tomum ehren- . -,..., itii 



bergi; n. gang- branches. In summer time one can often distinguish several dark-brown, 

 small spheres on each side of the body. These are the eggs, or more cor- 

 rectly the egg-capsules, which are deposited on aquatic plants. In reality each capsule 

 contains several true eggs, which are very soft and delicate, and a certain quantity of 

 nutritive material deposited around the eggs, to be gradually absorbed by the latter, and 

 used as raw material to build up the structure of the embryo. The interesting manner 

 by which the Mesostomum preys on Daphnias and Cyprids is thus described by Oskar 

 Schmidt : — "It captures them as one might capture a fly with the hand, for it closes 

 the hind extremity against the front, and by bending over the edges of the body forms 

 a complete cavity ; at first its captured prey rushes madly about, but soon the Mesos- 

 tomum succeeds in fastening its powerful proboscis upon its prisoner. The struggles 

 of the Daphnia gradually cease ; its vampyre then stretches itself, and crawls away, 

 having sucked the life-blood of its victim." 



The second species is very common, be'ng often found upon the well-known 

 aquatic plant Utricularia. It measures scarcely an eighth of an inch in length, and 

 is remarkable for its bright green color, so uncommon among animals ; its anterior 

 end is somewhat pointed or conical. This I believe to be the Vortex viridis of 

 European naturalists. It is remarkable for its gregarious habits, large numbers being 

 found together. 



Although there are many genera and more species of this group known to natural- 

 ists, both from fresh and salt water, there is little in their habits to awaken general 

 interest. We will therefore close our account by a brief mention of the genus Con- 



