MICROHYDRA DURING I907. IO7 



EXPLANATION OF PLATES. 



The subjects of these plates have been greatly but very variously 

 magnified, and of course nothing can be learned by comparing them. 



PLATE I. 



Figure i. As drawn this represents a mature, ])icapitate Microhydra. 

 Either end with the l)ase may be understood as representing its single 

 upright condition when first attache<l, when it measures about one-half a 

 millimetre, or one-fiftieth of an inch, in height ; (b.) is the base or pedal 

 disc ; (c.) the capituhun crowned with lasso or thread cells. When mature 

 it most frequently ])ranches near the base, becoming about one milli- 

 meter, or one-twenty-fifth of an inch, from end to end. A third or 

 fourth branch is sometimes seen. 



Figure 2. A highly magnified median section (by Dr. J. A. Ryder) 

 showing the initial condition of the larval bud, or asexual larva, (l.b.) of 

 this hj'droid occupying about the middle third of its length. 



FigTires 3 to 7. Show the serial changes in size and position of the 

 larval bud (l.b.), as seen during seven or eight hours, until the helpless 

 larva (1.) drops off and drifts away as described. 



Figures 3 and 4. Show at both the oral extremities where they have 

 been disgorged, and in groups over other surfaces, the indigestible setae 

 (bristles) of worms, the hydroid has recently been seen to swallow. 



PLATE II. 



Shows the Microhydra, as it has frequently been seen, swallowing 

 or attempting to swallow, worms (w.) far larger than itself ; — in both these 

 cases failing to "stomach" the whole worm, it broke off at a natural 

 line of transverse segmentation, when the unburied " remains " escaped 

 alive, or dead. 



Figure 4. A verj' small hydroid had captured by the head a worm 

 apparently a dozen times its own length and nearly its own diameter : 

 how much had "gone down " when first seen we could only guess, but 

 probably a full meal for both branches ; but the remainder of the worm 

 wriggled aroimd until its tail was caught by the other head, after which 

 a long battle was waged, whose result remained problematical until a 

 transverse segmentation, as in the former case, released the hinder part 

 of the body, which ultimately broke loose near the tail, and the headless 

 and tailless worm " lapsed into obscurity." 



