. Le bulletin biologique. Biologie ; zoologie ; biologie marine. Détermination EN CEREBRATULUS 321 embryons ont été colorées, la partie supérieure, la plupart des espèces animales de l'ensemble de la bande (avec une exception probable, voir ci-dessous) contiennent des granules de bleu, et lorsque les cellules végétatives avait été souillé, la couleur était limitée plus ou moins à la partie inférieure, la partie végétative de la bande. Il est très difficile de tracer la limite de la zone tachée avec certitude dans Cerehratulus, mais je pense qu'il est évident que la bande cilié est composé de deux documents de l'animal et les cellules végétatives. Il a été observé dans plusieurs cas

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. The Biological bulletin. Biology; Zoology; Marine biology. DETERMINATION IN CEREBRATULUS EMBRYO 321 were stained, the upper, most animal part of the whole band (with one probable exception, see below) contained blue granules, and when the vegetative cells had been stained, the color was restricted more or less to the lower, vegetative part of the band. It is very difficult to trace the limit of the stained area with certainty in Cerehratulus, but I think it is evident that the ciliated band is composed of material both from the animal and the vegetative cells. It was observed in several cases that on one day the young pilidium showed the ectoderm, including the ciliated band, bluish (staining of the animal cells); the next day the stomach too had turned blue. It was noted, however, that the oesophagus and the inner sides of the lappets were still unaffected by the Nile blue. Thus it would appear that we are not dealing with a general diffusion of the stain. It seems probable that at this stage the stomach acts as an excretory organ, as is the case with the digestive tract of turbellarians (Westblad, 1923).. Fig. 3. In the 16-cell stage the four most animal cells, ani, were isolated, vitally- stained and transplanted back on the an2 cells. The animal fragment was probably rotated 180° at the transplantation: note the little patch of ciliated band too high up on the posterior side. Normally it probably constitutes the most anterior part of the band. Stained area stippled. Staining of the four veg2-cells of the 16-cell stage resulted in a blue stomach. Whether a small part of the veg2-material is or can be used to form a part of the oesophagus I cannot tell, —the limit of the stained area was not sufficiently sharp. Also in staining the four ani-cells I had great difficulties in observing the colored line. It seems to me that these four cells form the greater part of the pretrochal ectoderm down to about the equator of the pilidium. Thus an2 would form the ectoderm