ZOOLOGY. 305 
[Agassiz’s original statement about the young turtle is in his 
Contr. Nat. Hist. U. S., i, p. 175 (1857) and is as follows:—In 
‘speaking of the ‘‘ Succession of Characters” he says “ The Snap- 
ping Turtle, for instance, exhibits its small, crosslike sternum, its 
oot note he further adds, “ Pr. M. v. New-Wied quotes as a re- 
markable fact, that the Chelonara serpentina bites as soon as it is 
hatched. I have seen it snapping in the same fierce manner as it 
does when full-grown, at a time it was still a pale, almost colorless 
embryo, wrapped up. in its foetal envelopes, with a yolk larger 
than itself hanging from its sternum, three months before hatch- 
ing.” — Eprrors. | 
THE ÅFFINITIES OF Crinoips. — Metschnikoff, to whom we owe 
So many embryological’ investigations, has published preliminary 
notices * of the early stages of Comatula which are of the utmost 
importance, as they throw an entirely new light on the affinities of 
the Crinoids. > Thoroughly familiar with the pluteus of Holothu- 
rians, Echini, Starfishes and Ophbiurans, he commenced the inves- 
tigations of their earlier stages with the determination of tracing 
the presence of the peculiar water system of the larvæ of the 
other orders of Echinoderms; what had been previously written 
by Busch, Allman aud Thomson, on the early stages of Comatula, 
giving no date whatever bearing upon the subject. 
To his surprise he found no such water system, nor could he 
trace anything in any way homologous to it; he also discovered 
that what constitutes the water-system of adult Crinoids, which 
has always been homologised with the water-system of other Echin- 
ms is developed in a totally different manner. In the free 
Swimming Comatula larva the bag-like digestive sac is the only 
organ developed, it becomes the digestive cavity of the adult after 
larva attaches itself to the ground. He noticed the tentacles 
as diverticula of the digestive sac in the interior of the larva; 
. Se subsequently force their way through to the exterior, at the 
time when the digestive bag has become further differentiated, and 
1S provided with a mouth opening in the centre of the oval disk, 
and an anus opening not far from it on the side of the calyx. There 
* Bulletin Acad. St. Petersburg, xv, p. 508, February, 1871. 
AMER, NATURALIST, VOL. VI. 0 
