REPRODUCTION, VEGETABLE (VEGETABLE OVUM). 



257 



* In the zoosporous Algae, constantly recurring series of unisexual generations are produced indefinitely. 

 In Vorticella the production of Monads may also recur repeatedly, without the intervention of any 

 sexual stage. So long as this is the case the two developments correspond completely. 



Here it may be observed that in the stage 

 of cessation of growth, which, in the Pro- 

 tozoon, as well as in the Protophyton, follows 

 the act of conjugation, we have a condition 

 which corresponds to that of the ovum of 

 the higher animals. The ovum after passing 

 through a period of repose, resembling that 

 which presents itself in Podophrya, exhibits 

 a series of transformations, which correspond 

 to the later steps of the developments under 

 our consideration. This correspondence is, 

 as might be expected, more distinctly seen in 

 the lower than in the higher animals. Thus 

 for example, in the development of a Trema- 

 tode Worm (Distomum pacificum), the mass 

 of the yolk is transformed into a locomo- 

 tive rudiment resembling an infusory animal. 

 Within this originates an asexual, but fertile 

 nurse, the homologue of the Vorticella, in the 

 interior of which is formed a second and 

 numerous generation of animals endowed 

 with locomotion (Cercariae). In these, after 

 a time, the locomotive power is lost, and each 

 finally becomes a sexual Distomum.* 



Although the foregoing homologies are 

 founded on observations the details of which 

 are as yet imperfectly worked out (on which 

 account it may seem somewhat premature to 

 draw attention to them), they are not open to 

 the objections which may be urged to homo- 

 logies supposed to exist between the highest 

 members of the two series. There, the con- 

 necting links are wanting; here, we pass 

 through closely related intermediate forms, 

 from the Alga to the Protozoon, and from 

 the Protozoon to the Trematode Worm. 

 Hence, while we are not justified in applying 

 the term ovum to the generative product of 

 the phanerogamous plant, the present state 

 of our knowledge allows us with propriety 

 to compare with the ovum the result of con- 

 jugation as it occurs among the Algae. 



The differences in chemical composition 

 which exist between the Algae and the Pro- 

 tozoa will not serve as a ground of distinc- 

 tion. Euglena is invested during its period 

 of repose with a cellulose membrane and 

 contains granules of chlorophylle. In Poly- 

 toma uvella we find, on the one hand, the 

 contractile vesicles of the infusory animal, 

 on the other, starch in the granular form, 

 so characteristic of the plant-t 



(J. Bur don Sanderson.) 



* Cams, " System der Thierischen Morph.," s. 329. 

 t A. Schneider, "Beitrage zur Entwick. der In- 

 Supp. 



BIBLIOGRAPHY. ALCLE. Kohlreuter, Das en- 

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FUNGI AND LICHENS. Malpighi, De Plantia 

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PHANEROGAAIIA. Camerarius, Dissertatio de re 

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The reader is further referred to various researches 

 contained in the 3rd Series of the Ann. des Sc. Nat. 



fusorien," Mtiller's Archiv. No. 2. 1854. These re- 

 searches we recommend to the reader's attention, 

 as containing observations of great importance in 

 relation to the present question. 



