20 T. B. ROSSETER ON DREPANIDOT.ENIA VENUSTA. 



evolves itself into a perfect tapeworm. This paragraph of 

 Leuckart's exactly expresses what I should myself have written 

 as to the stage these Cestode ova attained, previous to their being 

 swallowed by a crustacean to become in its body cavity "a 

 cysticercus." But the uterine egg of Brep. venuskt (Figs. 12, 13, 

 14, 15 and 16), that is to say the six-hooked brood, passes from the 

 usual microscopic ball through successive stages, until it arrives 

 at a stage which reminds one very forcibly of that of the encysted 

 larval stage of Dihothridce, such as the Bothriocephalus larvae 

 found in the smelt or, when straightened out, to a young bladder- 

 worm of Tcania serrata or Cysticercus j^isiformis found in the 

 liver of the rabbit. Indeed, the uterine embryos in the ripened 

 segments of the latter Taenia are so far advanced in development 

 that there is seemingly but a stage between it and what the 

 3^oung bladder- worm will be as a Cysticercus 2nsiformis. I have 

 never traced the larval form in the ovum, as one finds it in the 

 hydatid ; but this I do know, that this elongation or pyriform 

 state does not take place until after the ova of Tcenia serrata has 

 "been swallowed by the rabbit. In like manner up to the present 

 time I have never seen the ova of avian cestodes change to a 

 form so similar to that which we find in the later stages of the 

 cysticercus of Drep. gracilis, minus the hooks and suckers, as these 

 uterine embryos of Drep. venusta. I would more particularly 

 <iall attention to the development seen in Figs. 14, 15, 16, to 

 illustrate the above remarks. I have no wish to beg the question, 

 l)ut the inferences one feels tempted to draw from this advanced 

 .stage in the metamorphosis of the ova of Drep. venusta, before it 

 enters the body cavity of the Cypris to become a cysticercus, are 

 not, from observations made by me up to the present time, 

 sufficiently matured for me to draw any parallel, or express an 

 opinion as to their differentiation. Morphologically it is sufficient 

 to serve as a note, or reference, in any future researches that may 

 be made in connexion with the development of the ova of the 

 Tseniadoe. The oncosphere is oval, its length, including the capsule, 

 is 0047 mm., breadth O'OSO mm. The embryo (Figs. 15, 16) is 

 approximately 0-034 mm. in length, breadth 0*020 mm. The 

 six hooks of the oncosphere (Fig. 17) measure individually 

 0-009 mm., a—h, 0-006 mm., a—c, 0-009 mm. 



The calcareous corpuscles are scarce in young segments, but 

 when the segment becomes gravid they range themselves vei-y 



