ON THE DEVELOPMENT OF LINGULA ANATINA. 9 



shape was used to attach larvre according to Patten's method 

 (Zeit. wiss. Mikr. Bd. XI., 1894. p. 13-15). The plate proved 

 better than a piece of granulated paper on account of its trans- 

 parency and its being easily detached from the paraffin block. 

 I prefer gelatine to the glass slip proposed by Hoffmann (Zeit. 

 wiss. Mikr. Bd. XV., 1898. p. 312-316.) for the same purpose, 

 as gelatine is easily marked with a knife. 



My present studies on the embryology of IAngula have 

 naturally been divided into two parts. The studies from the egg 

 up to the oldest embryo I obtained by rearing the egg, constitute 

 the first part ; those on the free-swimming larvœ and young 

 sedentary Lingula obtained by keeping the latter, the second part. 



A. EMBRYONAL STAGES. 

 IV. MATURATION AND FERTILIZATION. 



In describing the phenomena of maturation I shall begin 

 with the ovum which has just been deposited, and is at a stage 

 slightly prior to the casting out of the polar bodies. The ovum 

 (PI. IL, Fig. 14.) is spherical, its diameter measuring 90 ,«-100 /*, 

 just the same size as the largest yellow yolk-granules of the lien's 

 egg. It is enclosed by a thin vitelline membrane, a covering 

 apparently secreted from the surface of the ovum, while floating 

 either inside or outside the body, since no trace of it could be 

 found in eggs still enclosed in the follicle. Needless to say, it 

 is formed before fertilization. Under a high power the membrane 

 shows radial striations. In the ovum one may distinguish the 



