353 



which the joints remain permanently attached. We know nothing 

 further regarding the history of Catena except that it has been 

 found as indicated in the figure here reproduced from Schmarda. 



Among the Dendrocoela, or Planarians, and in fact in the flat 

 worms generally, fission takes place. If we cut the common fresh 

 water Planarians into several pieces, each piece will become a 

 perfect worm. 



All the fresh water flat worms are born as infusorian-like cili- 

 ated bodies which attain maturity without any metamorphosis. 

 As an example of the mode of development of a Planarian worm, 

 may be given the history of Planocera eUiptica discovered by 

 Girard in Boston and Beverly harbors. The spawning time lasts 

 from the middle of May until the middle of June, the eggs being 

 deposited in a thin viscid band on stones and sea weeds. The 

 egg undergoes total segmentation in four or five days after. A 

 ciliated blastoderm begins to form around the yolk mass, and be- 

 fore the embryo leaves the egg it assumes the larval shape, being 

 an infusorian-like form, with a caudal flagellum. There are no 

 internal organs except two eye-specks. 



In eight or ten days after the larva begins to revolve in the egg, 

 and after it has hatched, it stops swimming about and becomes 

 a "mummy-like body" which Girard calls a "chrysalis." In this 

 condition, which apparently corresponds to the encysted state of 

 the flukes, it floats about in the water. Here Girard's observa- 

 tions came to an end. Whether in this resting stage it is swal- 

 lowed by some other animal, and becomes a parasite before 

 resuming its active life, remains to be seen. 



The later history of Flanaria angulata has been traced by Mr. 

 A. Agassiz. "On examining," he says, " a string of eggs, mistaken 

 at first for those of some naked mollusk, I was surprised to find 

 young Planariaj in different stages of growth with a ramifying 

 digestive cavity, somewhat similar to that of adult specimens, but 

 showing besides, one distinct articulation for each spur of the 

 digestive cavity. The eyes were well developed, and when the 

 young became free, the articulations were still distinct." In the 

 youngest specimen (Fig. 162) observed, the body was almost 

 cylindrical, while as seen in Fig. 163, the body has become con- 

 siderably flattened. The fact that before attaining maturity the 

 Planarian is articulated is Very significant, showing that these 

 low worms, non-segmented in maturity, should not be excluded 



