The gonophore is now reduced to its simplest condition, known as the sporosac (fig.
That the sporosac should not be compared simply with the manubrium of the medusa, as is sometimes done.
The endodermal spadix (sp) of the sporosac represents the endoderm of the manubrium; the ectodermal lining of the sporosac (ex.) represents the ex-umbral ectoderm of the medusa; and the intervening layers, together with the sub-umbral cavity, have disappeared.
Each such sporosac has two long tentacle-like processes thickly ciliated.
Allman, however, regarded this type of gonad as equivalent to a sporosac, and considered the medusa bearing them as a non-sexual organism, a " blastocheme " as he termed it, producing by budding medusoid gonophores.
In the sporosac, however, the medusa-individual has become so degenerate that even the documentary proof, so to speak, of its medusoid nature may have been destroyed, and only circumstantial evidence of its nature can be produced.
Huxley, the sporosac is the starting-point of an evolution leading up through the various types of gonophores to the free medusa as the culminating point of a phyletic series.
Sporosac springing from the hydrocaulus.
Sporosac springing from m, a modified hydriform person (blastostyle): the genitalia are seen surrounding the spadix or manubrium.