[ 307 J 



ART. XXX. — Emhrijonic Development of Planocera elliptica. 

 By Charles Girard. 



PRELIMINARY REMARKS. 



The observations recorded in the present Memoir were made chiefly in the sprino- 

 of 1849, while assisting Prof. Agassiz in embryonic investigations upon several other 

 types of the animal kingdom. The microscope used was his large Oberhauser. 



A historical sketch of these investigations was read before the American Association 

 for the Advancement of Science, at its Cambridge meeting'in August 1849, and printed 

 in its Proceedings in 1850.* 



I then contemplated publishing without much delay the whole of my Researches 

 upon the American Nemertians and Planarians, together with the embryology of their 

 different types. But the time which I could devote subsequently to these investiga- 

 tions having become, by necessity very much limited, and fearing that the chief object 

 which I had in view in tracing them, and which was the starting point to new re- 

 searches, would lose its actuality, I determined to issue these as a first part. 



The species, the eggs of which constitute the subject of this memoir, is quite abundant 

 in the harbors of Boston and Beverly, Mass., under the stones of the beach, where I 

 have first observed it in the spring of 1847, and was since described by me under the 

 name of Planocera elliptica. I am inclined to think that its range may be found to 

 extend further north and likely also further south. 



All the drawings, except figs. 94 — 103, have been executed by myself from specimens 

 under the microscope ; the latter were made by Mr. A. Sonrel, from two models 

 which I furnished him, representing the young Planaria immediately after its escaping 

 from the egg. My original drawings have been admirably well reproduced on stone 

 by the above named artist. 



C. Girard. 



Cambridge, Mass., September 1850. 



*Proc. Amer. Assoc. Adv. Sc; 2d meeting 1849 (1850), 398, a French version of which subsequently appeared 

 in the " Bulletin de la Societe des Sciences naturelles de Neuchatel (Switzerland), vol. ii. 1850, 300. 



