568 
PEOFESSOB ALLMAN ON THE STETJCTUEE 
gonophores, and claspers, all different forms of zooids, each endowed with its own 
special function in the physiological division of labour, and all associated into a com- 
pound colony which forms the proper zoological Individual, the logical element of the 
species*. In Hy dr actinia we have hydranths, blastostyles, gonophores, and “spiral 
zooids ” similarly associated. In Hydractinia , however, there is a common coenosarcal 
basis which gives origin to many hydranths, as well as to the blastostyles with their 
gonophores, and to the spiral zooids ; while in Myriothela the hydranth is solitary, and 
the blastostyles and claspers are budded off from this. 
It will be seen that the account here given of the development of Myriothela offers 
no support to the view that the generative elements originate in certain cells of the 
ectoderm — a view which has been defended by Kleinenberg, who, in his excellent 
memoir on the structure and development of Hydra , maintains that both ova and 
spermatozoa have their origin in what he calls the “ interstitial tissue ” of the ectoderm. 
Neither does it support the view more recently put forward by Ed. van Beneden in his 
valuable memoir on the origin of the testis and ovary f. According to the Belgian 
zoologist the ova in Hydractinia always originate in the endoderm, while the sperma- 
tozoa just as constantly have their origin in the ectoderm. To this observation 
M. Ed. van Beneden attributes great significance ; for by adopting the highly probable 
hypothesis enunciated many years ago by Huxley, that the ectoderm represents the 
outer layer of the blastoderm in the higher animals and the endoderm the inner layer, 
he generalizes the results of his observations on Hydractinia, and maintains that 
throughout the animal kingdom the female generative system is a product of the inner 
leaf of the blastoderm, and the male of the outer leaf. 
From the observations on Myriothela , however, recorded above, it would seem to 
follow that both ova and spermatozoa originate in a special chamber which has become 
excavated in the substance of the endoderm, and that the ectoderm has nothing to do 
with either. 
I believe this to be the legitimate conclusion to be drawn from the appearances pre- 
sented. At the same time I admit that other observers may put a different interpre- 
tation on these appearances ; for it may be asserted that the material which is to become 
developed either into spermatozoa or into ova is in one or both cases a product of the 
ectoderm, and that it has subsequently to its origin migrated into the endoderm ; while 
in proof of this the orifice which exists in the roof of the endodermal chamber will 
probably be adduced and maintained to be the channel through which the generative 
elements have gained access to this chamber. 
Knowing the memoir of M. E. van Beneden, in which he maintains that the spermatic 
* The terms Zooid and Individual are used here with the significations originally proposed hy Huxley. 
The former is the “ Individual of the fifth order, Person ” of Haeckel, the latter the “ Individual of the sixth 
order, Stock or Cormus ” of Haeckel. 
Eduard van Beneden, “ De la Distinction Originelle dii Testicule et de l’Ovaire,” Bull, de l’Acad. Boy. de 
Belgique, 2 ° serie, tome xxxvii. no. 5, Mai 1874. 
