556 THE ANATOMY OF INVERTEBRATED ANIMALS. 



continued into the vagina (Fig. 157, C). The uterus passes 

 above into a short, open, funnel-shaped canal, which lies be- 

 tween the two oviducts (Fig. 157, C c), and, according to Von 

 Siebold, takes in the ova from the perivisceral cavity by a pe- 

 culiar swallowing action. 



The embryos of the different species of Echinorhynchi 

 vary somewhat in structure. Von Siebold has described those 

 of E gigas, which are provided with hooks disposed like those 

 of the Cestoidea, but only four in number. Sexless Echino- 

 rhynchi have been found in Cyclops and in the muscles of 

 fishes. Leuckart states that they acquire sexual organs in 

 the alimentary canal of Gadus lota. The same excellent ob- 

 server has succeeded in tracing the development of Echino- 

 rhynchus proteus, a common parasite of many river fishes, es- 

 pecially the Perch. 1 What appeared to be the sexless con- 

 dition of the same Echinorhynchus had previously been seen 

 by Leuckart in Gammarus pulex. Into water containing 

 specimens of this Crustacean, ova from E. proteus were trans- 

 ferred. After a few days these ova could easily be detected 

 in the digestive tube of the Gammarus, while numerous em- 

 bryos, escaped from the egg-shell, were found within the ap- 

 pendages of the Crustacean. 



Each ovum has two coats — an outer, albuminous, and an 

 inner, chitinous. The first is digested in its progress through 

 the alimentary canal ; the second is afterward ruptured by 

 the embryo, which bores through the intestinal walls into the 

 cavity of the body, and is thence conveyed to the site proper 

 for its development. 



The body of the embryo is somewhat fusiform in shape, 

 and consists of a colorless, transparent parenchyma, protected 

 by a cuticle. The parenchyma may be resolved into an outer, 

 homogeneous, contractile layer, and a semi-fluid medullary 

 substance. Within this is lodged an ovoid, central mass, 

 made up of large, highly-refracting granules. Isolated gran- 

 ules of the same kind may also be found scattered throughout 

 the soft medullary substance. At its posterior end the em- 

 bryo tapers to a point, while its opposite extremity is obliquely 

 truncated toward the ventral aspect. On this oblique surface 

 may be observed two series of straight spines, five (rarely six) 



1 " Ueber Echinorhynchus " (" Gottinger Nachrichten," 1862). Results of 

 further investigations and a history of the subject are contained in Leuckart' s 

 " Programm," " De statu et embryonali etlarvali Echinorhynchorum eorumque 

 metamorphosi," 1873 ; and, further, in the concluding part of" Die mensch- 

 lichen Parasiten," 1876, which has reached me too late for use in this place. 



