94 MORPHOLOGY. 



present little or no trace of a spadix ; and if this ever existed, it must have been depressed at an 

 early stage by the ovarian plasma, which now lies upon an even floor of endoderm. 



The contents of these bodies consist in an early period of development of minute spherical 

 cells distributed through a semifluid granular blastema, and generally exhibiting a distinct 

 nucleus. As this cellular and granular material increases in volume, we find it becoming broken 

 up into detached masses. These masses vary much in size and form ; they frequently present a 

 veiy irregular outline, with projecting lobes and processes of no definite or permanent shape. At 

 a somewhat later period some of them burst through the confining wall of ectoderm, and then 

 usually remain for some time in the form of irregularly spherical bodies, attached to the external 

 surface of the gonophore, as if by the adhesive properties of their constituent blastema. 



The escaped masses may usually be seen to be themselves composed of au agglomeration of 

 smaller masses, reminding us of a segmented vitellus ; but I am, nevertheless, not prepared to 

 regard this complex condition as a true vitelHne segmentation. Further, no appearance of 

 a germinal vesicle or spot can at any time be detected in any part of the ovarian plasma, and yet 

 I believe we should not be justified in denying to the masses which have become detached the 

 significance of true ova.' 



Beyond this point my observations have not extended, but other observers have described 

 the liberated masses as enveloping themselves with a tough membrane, which in some species 

 would seem to develop over its surface peculiar forked spines. On the rupture of this membrane 

 its contents become directly developed into an actiniform embryo, which gradually assumes the 

 form of the adult Hydra." 



The resemblimce between the embryonic development in Hydra and that in Tubularia is thus 

 very close ; indeed, it is impossible not to regard them both as presenting the same essential 

 modification of the reproductive process — a modification whose most striking feature shows itself 

 in the formation of an actinula instead of a planula. 



I have had no opportunity of studying the genus Myriothela of Sars ; but from the observa- 

 tions of Mr. W. P. Cocks, who was the first to meet with this remarkable hydroid genus on the 

 British shores, as well as from those of Mr. Joshua Alder, it would appear that actiniform embryos 

 closely resembling those of Tiihidaria are the immediate result of the development of the ovum. 



Several years ago M. Van Bcneden described and figured a Cori/ne-Y\ke, hydroid from the 

 coast of Belgium, and assigned to it the name of Syncoryne pusilla, under the belief that it was 

 identical with the original Coryne pusilla of Gaertner.* In this determination M. Van Beneden 

 was wrong ; but his hydroid possesses special interest from the nature of its gonophores, which 

 are described as giving origin to actinula-like bodies, whose form is compared by the Belgian 



' Rouget, who has examined with much care the reproductive system of Hydra (' Mem. de la 

 Soc. de Biologic,' torn, iv, 1852, p. 387), compares these masses to a Graafian vesicle rather than to a 

 true ovum. 



" Pallas, ' Karakteristik der Thierpfiansen,' p. 53; Elirenberg, ' Abhandl. der Berl. Akad.,' 1836, 

 p. 115, taf. ii Laurent, ' Froriep's Neue Notizen,' No. 513, p. 10] ; and ' Nouveaux Recberclies sur les 

 Hydrcs d'eau douce, Voyage de la Bonite,' 1844. See also ' Ou the Generative System of Hydra,^ by 

 Prof. Allen Thomson, loc. cit., and Hancock, " Notes on a Species of Hydra found in the Northumber- 

 land Lakes," in the 'Annals of Natural History,' vol. v, 1850; and more especially Ecker, 'Eutwick- 

 elungsgeschichte dcs Griinen Armpolypen,' Freiburg im Breisgau, 1853. 



^ Van Beneden, ' Embryogenie des Tubulaires.' 



