DEGENERATION PHENOMENA IN THE 

 LARV.E OF GONIONEMA. 



HENRY FARNHAM PERKINS. 



Every student of invertebrate embryology has experienced the 

 difficulty of rearing eggs and larvae of marine animals with a view 

 to determining the stages in the life-history of the species. One 

 of the chief contingencies to be encountered is that which arises 

 from the necessity of supplying an artificial environment which 

 approaches closely enough to the natural conditions to permit the 

 creatures to live and thrive in captivity, and to develop normally. 

 In the effort to secure these favorable conditions many failures 

 are to be expected, and it frequently happens that remarkable 

 monstrosities are produced by some untoward condition which 

 can frequently be only guessed at. Interesting and significant ten- 

 dencies are sometimes to be traced in these abnormal forms, and 

 light is thrown upon the normal constitution of the tissues and 

 their power of assuming a variety of forms. 



The transforming and regenerative power which is displayed 

 by ccelenterate tissues has been adequately demonstrated by in- 

 vestigators in various orders. Among the hydroids, several in- 

 stances have been recorded in which the soft parts of the colonies 

 exhibit amcebiform activity. In Hydra, when live specimens are 

 mounted in water under a cover-glass, so that the tentacles are 

 in contact with the glass, their tips are frequently seen to become 

 spread out in a smear against the glass, and flowing movement is 

 observable in the protoplasmic tissue-layers. It may be added 

 that the same activity occurs in the tips of the tentacles in the 

 Hydra-\\ke polyps of Gonioncina, which furnish the data for the 

 present paper. 



In Plnimilaria cristata the soft internal substance of the colony, 

 the sarcode, flows out of the vase-like nematophores which are 

 borne upon the ramuli of the zooids, and after being protruded 

 for a short distance send out long filamentous pseudopodia ; 

 these frequently branch and anastomose, like the pseudopodia, of 

 the amoeba. The processes are afterwards withdrawn again into 



172 



