Fio. 43. Stages in the de- 

 velopment of Dipylidium 

 run i a a, a L. ( = Taenia 

 elliptica Batsch, T. cvcu- 

 merina Bloch), the com- 

 monest of the Dog-Taeniae ; 

 compare Fig. 44. A, 

 Six - hooked larva (now 

 often spoken of as an 

 " Ouchosphaera "); B, 

 larva elongating ; forma- 

 tion of a central lacuna ; 



C, larva further advanced ; 



D, distinction between 

 body and tail is visible ; 



E, iuvaginatiou of the 

 rostellum is commencing ; 



F, Cysticercoid larva with 

 four suckers, invaginatecl 

 rostellum, and excretory 

 vessels, c, Calcareous con- 

 cretions in cells of the 

 larva ; ex.o, excretory 

 aperture ; ex.v, excretory 

 vessels ; inv, invagination 

 commencing ; rost, rostel- 

 lum ; sc, suckers. (After 

 Grassi and Rovelli; highly 

 magnified.) 



FIG. 44. Schematic longi- 

 tudinal sections 

 through the larvae of 

 Dipylidium caninum, 

 L. All these stages 

 are passed in the 

 body - cavity of the 

 Dog-flea (Pulex serra- 

 ticeps). (Compare Fig. 

 43 for further details.) 

 A, Six -hooked larva 

 with developing rostel- 

 lum (shaded) and 

 suckers (black). I 

 this species the invagi- 

 nation ( C, in vag. ) occurs 

 after the formation of 

 these organs, and not, 

 as in most Taeniae, before it. B, Invagination commencing ; the hooks are developing 

 above the rostellum, while beneath it the nervous system (dotted) is seen. C, The 

 invagination has now carried the suckers inwards. The tail has become distinct, and 

 the whole larva at this stage is known as a Cysticercoid. hk, Larval hooks ; invag, 

 mouth of the invagination ; n, central nervous system ; rost, rostellum and hooks ; sc, 

 suckers, of which only two can be seen in a longitudinal section ; four are really 

 present. (After Grassi and Rovelli.) 



