32 ZOOLOGY. 
on the other hand, itself brings forth a progeny, which returns in its form 
and nature to the parent atetals so that the maternal animal does not meet 
with its resemblance in its own rb ood, but in its descendants of the second, 
third, or fourth degree or Sonera and this always takes place in the 
different animals wiht exhibit the phenomenon in a determinate generation, 
or with the intervention of a determinate number of generations. This 
remarkable precedence of one or more generations, whose function it is, as 
it were, to prepare the way for the later succeeding generation of animals, 
destined to attain a higher degree of perfection, and which are developed 
into the form of the mother, and propagate the species by means of ova, 
can, I believe, be demonstrated in not a few instances in the animal 
Eitan?” ; 
5 6 
When a ee as queer aurita (pl. 76, fig 74), produces an egg, the 
progeny resembles an animalcule (Diagram, jig. 1), which moves in the 
direction of the arrow by means of vibrille. The anterior extremity has a 
round sucker (but not a mouth), by means of which, after several changes 
of form, it attaches itself to some extraneous object (Diagram, fig. 2). The 
changes still continue, the two projections at the free end are extended, a 
mouth is formed in the centre, and a second pair of projections arises 
between the first. About the fifth or sixth day the four tentacles have become 
longer, and the body quadrate, and the animal now constitutes the supposed 
perfect genus, Scyphistoma (Diagram, jig. 3), of Sars. In the next place, 
four additional tentacles arise between the four earlier ones, and this 
production continues until the number equals twenty-eight or thirty, and by 
this time the animal resembles a polyp. 
In the subsequent changes an entirely new phenomenon is observable. 
The free extremity of the body begins to show indications of a division into 
segments, of which one is shown in Diagram, jig. 4; the length and 
number of segments increase, the body becomes cylindrical, and is now 
about a line in diameter (its original size being that of a grain of sand), the 
upper margin of the segments becomes free and divided into lobes 
(Diagram, po 5), capable a independent motion, when the form constitutes 
the supposed genus, Strobila, of Sars, named ane its resemblance to the 
cones of a pine tree. 
236 
