July 13, 1900.] 



SCIENCE. 



65 



shown by the sluggish movements and di- 

 minished vitality, while many had clear- 

 cut holes or ulcers, as described above. 

 Others appeared with the eyes entirely 

 gone ; in others great patches of skin and 

 underlying muscle tissue had fallen out, 

 leaving large irregular pits in the body 

 walls; others still had lost fins or lower 

 jaws, etc. 



Upon working out the life-history of the 

 parasite, it was found that spores accumu- 

 late in the lymph spaces of the fish and 

 prevent normal nourishment of the tissues, 

 which die and fall out leaving holes in the 

 body-walls. The spores are taken into the 

 digestive tract of the fish — it is not known 

 from where they came originally; in the 

 intestine they give rise to eight sporozoites 

 or germs each of which develops into an 

 adult amoeboid individual not more than 

 .001 inch in length. These adults penetrate 

 the bundles of unstriped muscle cells of the 

 intestine and there become mature. At 

 maturity a spherical spore-forming cyst is 

 formed in the lymph of the fish ; here also 

 the spores are liberated, and are then car- 

 ried to all parts of the body where at differ- 

 ent points the accumulations are formed 

 which lead to ulcers. 



Two very important points were not de- 

 termined viz, (1) the origin of the disease 

 which hitherto has probably been un- 

 known, and, (2) the remedy. There was 

 little chance of finding out after October 

 how the disease originated in May, while 

 the extinction of all the diseased fish be- 

 fore the parasite was even discovered effec- 

 tively headed off experiments with remedial 

 measures. Gaet IST. Calkins. 



EMBRYOLOGY OF LEPAS. * 

 This paper was based upon the results of 

 an investigation recently completed, which 

 * Abstract of a paper read before the Biological Sec- 

 tion of the New York Academy of Sciences, April 9, 

 1900. 



was undertaken with the view of applying 

 the cell-lineage method in an accurate study 

 of the cleavage and the formation of the 

 germ-layers in Lepa& and other Cirripedes. 



The cleavage of Lepas is total, unequal, 

 and regular. Stages of 2, 4, 8, 16, 32, and 

 62 cells are normally formed. Cells of a 

 given generation may anticipate their com- 

 panions in division, but no second division 

 of such cells takes place before all other 

 cells have completed corresponding cleav- 

 ages and become of the same generation. 



The first cleavage is nearly parallel to 

 the long axis (polar) of the ellipsoidal egg. 

 The egg is divided into an anterior ecto- 

 blastic cell and a posterior yolk-bearing 

 macromere. The second cleavage is at 

 right angles to the first, both cells dividing, 

 and from the yolk-macromere is cut off a 

 second ectoblastic cell. The third cleav- 

 age is essentially perpendicular to the first 

 two, dividing all the cells, and a third ecto- 

 blastic cell is separated from the yolk- 

 macromere, which is now mesentoblastic. 

 Thus by the first, second and third cleavages 

 three protoplasmic cells are separated from 

 the yolk. These three cells contain all the 

 ectoblast and by repeated division they form 

 and extend the blastoderm. The fourth 

 cleavage separates the mesoblast from the 

 entoblast, which is now represented by the 

 yolk-macromere. The 16-cell stage is com- 

 posed of fourteen ectoblastic cells, which 

 largely surround the entoblastic yolk-cell. 

 The single mesoblast cell lies in the blasto- 

 derm at the posterior edge of the blastopore 

 where the entoblastic yolk-cell is still ex- 

 posed to the exterior. By the fifth cleavage 

 all these cells are divided, the two meso- 

 blastic cells still remaining on the surface. 

 During the sixth cleavage the two meso- 

 blastic cells before dividing sink beneath the 

 blastoderm as it closes over the blastopore. 

 At the same time four cells of the blasto- 

 derm, lying at the anterior and lateral edges 

 of the blastopore, divide perpendicularly to 



