OTHER FORMS OF ALTERNATION. 178 



form is nowise opposed to this view, for we have seen a cor- 

 responding diversity in some polypes which form their ova 

 in free well-developed medusoids, but the spermatozoa in 

 simple attached cysts. 



§ 6. From such cases we pass by an easy transition to 

 the Cestoid Entozoa with voluminous caudal sesmients, of 

 later growth, containing the reproductive organs. In the 

 foregoing remarks these have been unhesitatingly considered 

 as gamomorphic zooids — a view adopted by Van Beneden 

 and others of the first authority in helminthology, and one, 

 as it would seem, fully borne out by their disproportionate 

 development, and their ultimate detachment while still re- 

 taining their vitality.* At the same time it must be ad- 

 mitted that they may also be regarded as being, for a time 

 at least, integral members of the vermiform body, from their 

 connection with each other and with the "head," by two 

 sets of so-called vascular canals and by continuity of tissue 

 generally. 



§ 7. It is ob"saous that if this gradation through the 

 Polyzoa, Lerneada, and Cestoidea, be admitted as showing a 

 community of nature between the ordinary development of 

 the reproductive organs in the majority of animals, and 

 well-marked cases of alternation of generations, we must in- 

 clude in our generalization all the gamomorphic zooids fall- 

 ing under the latter head ; so that even the large hood- 

 eyed Medusae must be regarded as representing the repro- 

 ductive organs of the small Lucernarian Polypes from wliich 

 they have been budded off — not being after all much more 

 disproportionate in size than the voluminous caudal seg- 

 ments of a large Tapeworm, in comparison with its minute 

 denticulated head. 



The same conclusion, indeed, as has been already shown. 



* Kiiclienmeister describes the joints as depositing their ova as they 

 wriggle along with a sori; of spontaneous movement. 



