ORIGIN AND TRANSFORMATION OF ANIMALS. 
237 
curious story, let us follow M. Quatrefages, and advert to a 
similar set of incidents in the domestic manners of the Me¬ 
dusae^ or jelly-fish. ‘‘For more than a century/^ as he tells 
uSj zoologists had admitted among the other great divisions 
of the subkingdom of the Radiata, the class of Acalepha, or 
Medusa (sea nettles, jelly-fish), and that of polyps. This 
distinction seemed more than justified, as differences between 
the two groups were detected, more profound and more 
numerous than those which separate the reptiles from the 
birds. There was, in fact, no resemblance in external aspect 
or internal organization. • The jelly-fish, or Medusae, for 
example, are free swimmers, and mostly solitary; while only 
a few polyps enjoy a crawling motion, nearly all are fixed, 
and most of them live in colonies. Notwithstanding these 
•and other differences, the two classes approximated as their 
history became known. “ The Medusa lays eggs, well cha¬ 
racterised by the existence of three concentric spheres, of 
which' we have already spoken. These eggs transform them¬ 
selves into larvae, which at first differ little from those of the 
Serpula or the Teredo. Their oval and apparently homo¬ 
geneous bodies are covered with vibratory cilia, and exhibit 
a small depression in front. They swim for some time with 
vivacity, like the Infusoria, which they resemble sufficiently 
to deceive any one whose observations were restricted. This 
first phase of the life of a Medusa lasts about eight and forty 
hours. The movements then grow slower, the young larvae 
seem fatigued, and by the aid of the little depression attach 
themselves to some solid body. Henceforth the wanderer 
vegetates in one spot—a thick mucus which it secretes 
forms a large disc, that fixes it firmly.* The young Medusa 
changes its shape as well as its mode of life. It elongates 
rapidly. Its pedicle grows narrower, and its free extremity 
swells out in a club form. Soon an opening appears in the 
middle of this extremity, and an internal cavity is seen. Four 
little nipples spring from the margin and grow into arms, 
while others are not slow to appear, and elongate in their 
turn. The infusory of yesterday is changed into a polyp.^’ 
In this state it exhibits the properties and ways of the polyp 
group, multiplying by buds and by stoleSy^ from which new 
polyps arise. The formation thus produced resembles “ horns 
widely expanded, but short, and having their margins gar- 
* In a note M. Quatrefages says that he has reproduced the opinion of 
Sars, although he thinks it probable that the so-called mucus is a veritable 
expansion of the sarcode. 
t “ Stole (siolo, a shoot)y a lax, trailing branch, given off at the summit of 
