320 Prof. Allman on Myriothela phiygia. 



12. The generative elements, whether male or female, ori- 

 ginate in a special cavity, which is formed in the substance of 

 the endoderm of the sporosac. 



13. In the female the primitive plasma becomes gradually 

 differentiated into a multitude of cell-like bodies having all the 

 characters of true ova with their germinal vesicle and spot. 

 They are entirely destitute of enveloping membrane. 



14. These bodies next begin to coalesce with one another 

 into numerous roundish masses of protoplasm, which develop 

 over their surface minute pseudopodial retractile processes. 



15. The masses thus formed still further coalesce with one 

 another ; and there results a single spheroidal plasma mass, 

 through which are dispersed numerous small spherical vesicles 

 mostly provided with a nucleus. These vesicles appear to 

 be nothing more than the nucleolated nuclei of the coalesced 

 ova-like cells. 



16. About the time of the completion of this last coalescence 

 the resulting plasma mass, enveloped in an external structure- 

 less membrane, is expelled by the contraction of the sporosac 

 through an aperture in its summit. 



17". Immediately after its expulsion it is seized by the 

 sucker-like extremities of certain remarkable organs (claspers), 

 which are developed among the blastostyles and resemble long 

 filiform and very contractile tentacles. 



18. It is apparently now that fertilization is effected; for 

 the plasma becomes again resolved into a multitude of round- 

 ish masses. This phenomenon may be regarded as represent- 

 ing the yelk-cleavage of an ordinary ovum. 



19. The mulberry-like mass thus formed, surrounded by its 

 structureless membrane, which has now acquired considerable 

 thickness, and forms a firm capsule, continues to be held in 

 the grasp of the claspers during certain subsequent stages of 

 its development. An endoderm and ectoderm with a true 

 multicellular structure become differentiated ; a central cavity 

 is formed by excavation; and the germ becomes thus converted 

 into a spheroidal non-ciliated planula. This, after acquiring 

 certain external appendages, ultimately escapes by the rupture 

 of the capsule as a free actinuloid embryo. 



20. The actinuloid, on its escape from its capsule, is pro- 

 vided not only with the long arms already noticed by Cocks 

 and Alder, but with short scattered clavate tentacles. The 

 short clavate tentacles become the permanent tentacles of the 

 fully developed hydroid ; the long arms, on the other hand, 

 are purely embryonic and transitory. 



21. The long embryonic arms originate in the spheroidal 

 planula. They are formed by a true invagination, and at 



