IN THE ANIMAL KINGDOM. 99 



effecting an entrance into the sudoriparous ducts of the 

 skin. Other Filar ice which do not develope sexual organs 

 may probably have a like origin. In the same way Kuchen- 

 meister and other writers are inclined to identify the Tri- 

 china spiralis with the Trichocephalus dispar ; but in re- 

 gard to this there is greater dubiety, as there is a certain 

 amount of evidence in favour of the Trichina developing 

 sexual organs of its own.* 



9. REPRODUCTION IN THE ANNELIDA. 



Though egg-like bodies with more than one embryo have 

 been met with in some Annelida, the probability is that 

 they are only nidimentary envelopes, such as are common 

 among the Gasteropoda, for we have no evidence of any 

 fissiparous or gemmiparous multiplication in this class, in 

 the protomorphic stage of development. -f- With the first 



* For a list of references on the development of Trichina, see Burnett's 

 note in his Transl. of Siebold's Compar. Anat., p. 31. 



The most recent researches are those of Leuckart, communicated in the 

 present year to the Royal Academy of Sciences of Gottingen. The re- 

 sults are as follows : 



The Trichina is the young state of a small Nematoid worm hitherto 

 unknown, but occurring in large numbers in the intestines of many Mam- 

 malia and Birds. It is introduced by the ingestion and digestion of the 

 flesh of the prey affected with the parasite, and very soon when set free 

 acquires full sexual maturity. The young are developed in about six 

 days, and immediately begin to make their way to the muscular tissues, 

 by penetrating through the wall of the intestine, and the peritoneal cover- 

 ing of the abdominal cavity. They make their way finally into the in- 

 terior of the ultimate muscular fibres, and there attain within fourteen 

 days the size and organization of the Trichina spiralis, as commonly met 

 with. The penetration of these embryos in large quantity sometimes gives 

 rise to dangerous peritonitis. Annals of Nat. Hist., 3d Ser., V., 504. 



f In some Nemertini, according to Desor and Schulze, the early develop- 

 ment somewhat resembles that of the Trematode Entozoa, for the first 

 formation from the egg is a ciliated infusorian, with a mouth-like cleft on 

 one side. Within this is generated an active vermiform body, which 

 eventually escapes from the matrix, carrying away the cleft mentioned, 



r2 



