52 



MARINE ANIMALS OF MASSACHUSETTS BAY. 



miferous tubes. (Fig. 64.) The tentacles are numerous, multi- 

 plying to about a hundred and ninety-two in the adult, and in- 

 creasing according to the numerical law to be explained in the 

 description of the Oceania. 



This little Jelly-fish is one of the most common in our Bay. 



Fig. 63. 



Fig. 64. 



There is not a night or day when they cannot be taken in large 

 numbers, from the early spring till late in the autumn ; and as 

 the breeding season lasts during the whole of that period, they 

 are found in all possible stages of growth. In consequence of 

 this, the course of their development, and the relation between 

 the different phases of their existence as Hydroids, and afterwards 

 as Acalephs, are well known, though the successive steps of their 

 growth have not been traced connectedly, as in some of the other 

 Jelly-fishes, the Tima or Melicertum, for instance. The process 

 is, however, so similar throughout the class of Hydroids, that, 

 having followed it from beginning to end in some of the groups, 

 we have the key to the history of others, whose development has 

 not been so fully traced. The eggs laid by the Eucope in the 

 autumn develop into planulae, which acquire their full size as 

 Hydroid communities toward the close of the winter, and the 

 development of the young Medusas upon them, as described 

 above, begins with the opening spring. 



Tig. 63. Quarter-disk of young Eucope, older than Fig. 62, with a second set of tentacles (2) be- 

 tween the first set (1). 

 Fig. 64. Magnified quarter-disk of adult Eucope. 



