THE ANNALS 
AND 
MAGAZINE OF NATURAL HISTORY. 
[FOURTH SERIES. ] 
CO reconoenaccomo per litora spargite muscum, 
Naiades, et circium vitreos considite fontes: 
Pollice virgineo teneros hic carpite flores: 
Floribus et pictum, dive, replete canistrum. 
At vos, o Nymphs Craterides, ite sub undas; 
Ite, recurvato variata corallia trunco 
Vellite muscosis e rupibus, et mihi conchas 
Ferte, Des pelagi, et pingui conchylia succo.”’ 
N. Parthenii Giannettasii Eel, 1. 
No. 85. JANUARY 1875. 
I.— Observations on Hiickel’s Gastrea Theory. 
By Dr. W. SALensky*. 
[Plate V. ] 
HACcKEL’s investigations on the Calcispongiz, which are 
brought together in his admirable monograph, have led him 
to a theory to which he ascribes great importance for the con- 
ception of the phylogenetic relations of the types of animals, 
and which he calls the Gastrwa theory. This theory was first 
presented in its chief features in the portion of the monograph 
treating of developmental history ; but Hickel has since pub- 
lished a special memoir upon it and expounded it much more 
in detail and with relation to the germ-lamella theory t. 
In its principal features this theory may be summed up 
very shortly. It consists chiefly in the statement that in the 
ontogenetic development of all the representatives of the vari- 
* Translated by W.S. Dallas, F.L.S., from the ‘Archiv fiir Natur- 
geschichte,’ 1974, pp. 187-174. 
+ Hack tastrea-Theorie, die phylogenetische Classification und 
die Home <eimblatter.’ 
Ann. N. Hist. Ser. 4. Vol. xv. 1 
