MEROCYTES AND BLASTODERM. 87 



and under varied and striking forms — albeit in a series more or less gradational 

 (/. c, showing more decided mitotic character) as one passes from a lower to a 

 higher zone in the yolk substance. To illustrate various types of division: In r, 

 in a sphere of fine yolk is a nucleus about to divide amitotically*; in s a similar 

 nucleus has undergone such a division, in this case four nuclei resulting. In a 

 somewhat similar case, t, noteworthy growth in two of the resultant nuclei has 

 occurred; thej' have, in fact, passed out of the sphere of finer into the coarser 

 yolk. In u three similar and large nuclei result. In v, which represents a later 

 stage of the condition shown in t or u, and is drawn similarly from deep in the yolk 

 region of a section {c. g., as seen at several points in k), continued amitosis occurs; 

 here one of the larger nuclei, especially, is seen to be budding off a small nucleus, 

 and it has already apparently budded off several. In w, a similar detail indicates 

 the great rapidity with which nuclei maj^ arise; a large nucleus at one point has 

 given off a small one, while at a neighboring point almost simultaneously (judging 

 from the close position of the small nucleus) it is budding out a long process which 

 is about to be separated not into a single new nucleus but into two. In x seven 

 nuclei have arisen from a single center (? sphere substance) in the fine j'olk, and of 

 these one has undergone rearrangement in its chromatin material. Of this a dense 

 mass occupies the center of the nucleus and is connected with the nuclear wall 

 by a series of radiating linin strands. In v a somewhat similar nucleus is shown in 

 detail; at one side it is apposed to the finer yolk (= ? sphere substance) and here 

 the mass of chromatin approaches, indeed almost touches the nuclear membrane 

 (for nutritive reasons?). In another nucleus, z, the chromatin mass shows a doubled 

 arrangement, preliminary, as it appears, to a stage in division shown in aa, ff, and 

 possibly in bb. In turn the doubled nucleus in cc is obvioush^ a further stage than 

 AA, but it shows also around it a series of (five) smaller nuclei which, from their 

 radiating arrangement around the dividing nucleus in the center of the fine yolk, 

 are possibly the descendants of a similar type of nuclear division. In dd a nucleus 

 shows a less distinct doubling of its chromatic elements than aa-cc. And in ee a 

 distinct threefold division occurs, gg represents a stage in division carried further 

 than cc, the neighboring nucleus having probably arisen from a similar division. 

 In HH are two neighboring nuclei, the products, we conclude, of a division like that 

 of GG and cc: but, curiously enough, the}' are undergoing division in different ways. 

 The upper, near which appears an attraction sphere and centrosome, has arrayed 

 its chromatin in two masses nearly equal in size, each suggesting a confused series 

 of chromosomes ; the lower is simply passing out a portion of its chromatic substance 

 into the fine j^olk. In 11, the last of the series given, two nuclei appear; they are 

 evidently products of such a division as gg, and each in turn is about to undergo 

 division. The lower one is noteworthy, since the division of the chromatin material 

 is practically completed in the middle of the nucleus. It may be said in general 

 that the nuclear processes which here approximate mitosis (cc or mi) are observed 

 in the region immediatel}' subjacent to the yolk entoderm. 



*A similar condition in the embryonic germ cells of Loligo appears to be due to rapid growth, and is not 

 followed by fragmentation (Miss Sturges, Science, 1899, Feb. 3, pp. 1S3-1S4). 



