370 SUMMARY OF CURRENT RESEARCHES RELATING TO 



secreted by the animal itself. He gave to these structures the name 

 HilfsJcammerivdnde. He writes against the change of this term into 

 pseudoseptnni, and against sundry misrepresentations both of his 

 discovery and of the facts of the case. 



Development of Sepia.* — M. L. Vialleton has a memoir on the early 

 stages in the development of this Cephalopod. The egg is at first a 

 simple nucleated cell, surrounded by a few flattened cells which form 

 a rudimentary follicle. This follicle soon becomes complicated, and 

 presents an inner epithelial layer, and an outer connective and lamellar 

 one. The former becomes folded, and begins to secrete the nutrient 

 yolk which does not mix with the protoplasm of the egg. The follicular 

 cells do not emigrate into the interior of the egg to serve as food, but 

 simply furnish it with their secretion. As the egg grows, the germinal 

 vesicle does the same, and undergoes considerable modifications ; its 

 contents, which at first consisted chiefly of chromatic material in different 

 stages of division, contain, later on, only a few chromatic grains dis- 

 tributed in a large mass of finely granular protoplasm. When the 

 follicular cells have secreted all the nutrient yolk necessary for the egg, 

 they provide it with a chorion. The germinal vesicle disappears. The 

 egg, now ripe, drops into the peritoneal cavity, but it is not fecundated 

 till it leaves the oviduct. 



The egg is expelled by the funnel, seized by the ventral arms and 

 buccal membrane, and fertilized by sperm from the copulatory pouches ; 

 it is then enveloped in its capsule, and fixed to submerged bodies. The 

 formation of polar globules takes place, no doubt, at the moment when 

 the egg is expelled. The two pronuclei are identical in structure, have 

 no proper separable membrane, but a very fine pellicle of chromatin ; 

 they fuse in the ordinary way. As they pass over the formative yolk 

 the protoplasmic granulations which inclose it group themselves around 

 the pronuclei so as to form the germinal disc. The formative yolk at 

 the periphery of the disc is a very delicate hyaline lamella, which 

 gradually fuses with the nutrient yolk. The first segmentation -nucleus 

 is near, but not exactly at the centre of the germinal disc. 



The first segmentation-groove is meridian, and divides the germinal 

 disc into two equal parts ; the next two grooves are likewise meridian, 

 and give rise to eight unequal segments which are arranged symmetrically 

 in relation to the first groove, which becomes the axis of the blastoderm ; 

 though unequal, these eight segments are all macromeres. The six 

 upper and lateral segments are next divided by a meridian groove, but 

 the two lower by an equatorial one ; the uppermost of the latter set 

 occupies the centre of the blastoderm, and its cells correspond to the 

 micromeres. Segmentation becomes more irregular. At the end of 

 segmentation the blastomeres (micromeres) are very numerous, as there 

 are more than three hundred present ; they form a circular plate limited 

 externally by the zone of blastocones. 



As development proceeds the differences between these two sets of 

 cells becomes more and more marked, till at last the blastomeres form a 

 multi striated cellular disc (blastoderm), while the blastocones have 

 scattered their nuclei throughout the whole extent of a hyaline layer, 

 which they thus transform into a multinucleated true plasmodium, the 

 perivitelline membrane. The blastoderm gradually covers this membrane, 



* Ann. Sci. Nat., vi. (1888) pp. 165-280 (8 pis.). 



