PLATE VII. 



Gemellaria implexa. 



Fig. 



1. A portion of a colon \', magnified. 



2. A colony, natural size, attached to a piece of rock. 



3. A planoblast sliortly after liberation, as it appears while floating passively in the water, very 



much magnified. The tentacular appendages are seen with their peduncles in various 

 states of extension. 



4. A marginal tentacle of the planoblast still more enlarged, and with the appendages entirely 



retracted. 



5. Longitudinal section of a portion of the hydranth showing histological structure : a, ectoderm 



with imbedded thread-cells ; b, muscular layer ; c, external large-celled layer of 

 endoderni; d, internal or glandular layer of endoderra immediately surrounding the 

 somatic cavity. 



6. One of the clavate sacs filled with thread-cells from the umbrella-margin of tiie 



planoblast. 



7. A thread-cell from the capitulum of a tentacle previous to evolution. 



8. The same after evolution. 



y. One of the large thread-cells from the ectoderm of the hydranth previous to evolution. 

 1 0. The same after evolution. 



