No. I.] GAR-PIKE AND STURGEON. 29 



radiate and villous layers ; its outer surface is irregular and 

 raised in projecting bosses of many sizes. The outer layer, 

 which may prove the equivalent of the gramdosa, is clearly the 

 adhesive envelope of the ^g^ : before immersed in water its 

 thickness is less than that of the combined inner layers ; its 

 structure is lamellar, and its specialized hygroscopic character 

 is doubtless the cause of its cellular elements being difficult to 

 distinguish. The glairy mass which the fertilized eggs give 

 off after some minutes' immersion in water seems clearly the 

 product of the outermost envelope. The writer, it will be 

 seen, differs in the interpretation of the ^gg membranes from 

 Mark, who regarded it " probable that the outer layer would 

 be found to correspond to the villous layer of the Gar-pike," 

 and "that the middle layer was simply the differentiated outer 

 half of the zona." The present writer is, however, by no 

 means convinced that the outer layer is to be regarded as the 

 granulosa, although he regards it probable. During the later 

 developmental stages, when partly detached and greatly re- 

 duced in thickness, it becomes most similar to the outer mem- 

 brane of the Gar-pike : its irregular thickened and distended 

 character during the period of the eggs' fixation may accord- 

 ingly prove a specialization of its outermost layers to acquire 

 an hygroscopic function, or may be even, but less probably, 

 due to a direct secretion of its glandular cells. 



The outward changes which the Q.gg has undergone by the 

 time of the first cleavage are not noteworthy. Sectioned at 

 this state the ^gg presents but slight differences from the con- 

 ditions of Lepidosteus, cf. PI. I, Fig. 21, and PI. Ill, Fig. 55. 

 The line of demarcation of the deutoplasm is less clearly 

 drawn and the deutoplasm itself is more coarsely granular, its 

 elements usually containing a store of more finely differen- 

 tiated yolk. The nuclei are seen dividing at a similar niveau, 

 and are larger, though less distinctly marked. In preparations 

 of all early stages the chromosomes are not readily determined. 

 Certainly the most characteristic feature of the e^gg is the 

 presence of abundant pigment : it is seen massed at the animal 

 pole as if in a vortex, its granules sinking in thread-like 

 clusters downward and outward. 



