396 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



in eacb egg is very small, although the number of eggs produced by this animal is euormous. At 

 Nassau, Palimirus begins to spawn in June. 



{d) CowyjarwoH.— Ishikawa describes very fully the ovaries and ovigenesis of the prawn At- 

 ■yejjhyra compressa and concludes that the ovum "originates from the inner lining of the ovary and 

 is at the beginning a cell with a nucleus and one, two, or rarely three nucleoli.' The mature egg, 

 according to this observer, has two membranes, one of which is due to the "hardening of the 

 peripheral protoplasm of the egg," while the other (secondary egg-membrane) is secreted by the 

 epithelial cells of the oviduct and added at the time the eggs are laid. 



There seems to be an error here in regard to the origin of the chorion. In the Decapod Crus- 

 tacea it is the rule that the choriou it secreted gradually during the growth of the egg by the cells 

 of the egg follicle. The large glandular cells found in the oviducts of Atyephyra possibly secrete 

 the viscid lluid by which the eggs are attached to the swimmerets, yet this point needs comfir- 

 mation. 



The chorion was found in the ovarian egg of Pagurns by Mayer (39), who says : 



Das Eierstocksei von Pagurus ist in der ersten Zeit seines Bestebens eine eehte Zelle niit Protoplasma, Kern und 

 Kern-Korpercbcn. Spiiter findet oine Einlageruug von Deutoplasma und die Bildung eiuer HUHe ans Chitin statt. 

 Eudlich wild der Kern unsichtbar; das Ei stellt dann eine Cytode vor. 



Das fertigo Ei verliisst den Leib des Krebses ohne Kern und mit einer Hiille versehen. 



This description answers for Alpheus in all essential points. 



The ripe egg of the crayfish (Astacus fluviatUk) is inclosed by a single envelope, the chorion. 

 According to Ludwig and Waldeyer it is not known whether this is a product of the egg or of the 

 follicle cells. Huxley (26) merely states that " a structureless vitelline membrane is formed between 

 the vitellus and the cells which line the ovisac." The ovisacs burst and the ova pass through the 

 ovary into the oviduct. When laid, the eggs " are invested by a viscous, transparent substance 

 which attaches them to the swimmerets of the female and then sets." Here as in other forms the 

 chorion is clearly the secretion product of the ovisac. 



In Granyon vulgaris Kingsley (31) finds that the late ovarian ova resemble the newly laid 

 eggs. There is a thin structureless envelope (choriou), but no trace of an inner vitelline membrane. 



Ludwig's general statement that the egg cells of ail Arthropods are surrounded by a vitelline 

 membrane (Dotterhaut), the product of the egg itself, is certainly erroneous. He divides the egg 

 membranes into primary egg membranes, those which are derived from the i)rotoplasm of the egg 

 itself or from its follicle cells, and secondary egg membranes, those formed by the wall of the oviduct 

 or otherwise. Balfour, following Van Benedeu, restricts the term vitelline membrane to structures 

 derived from the protoplasm of the ovum, and chorion to those formed by the cells of the follicle 

 or oviduct. In the categoiy of secondary structures would fall also those secreted by speci.al 

 glands, found, according to Ludwig, in Trombidium, Chilopoda, and nearly all Crustacea, and the 

 winter eggs of Daphnia and Tardigrada, which Is due to a moult or direct sex^aration of epithelium 

 from the body of the mother. 



In speaking of the vitelline membrane Van Beneden and Bessels, in their monograph on the 

 formation of the blastoderm (60), thus define it : 



Nous entendons la membrane vitelline dans le sens oii M. Claparcdo I'a si ncttement diSlinie dans son travail snr 

 les vers Nematodes : C'eet la concbe externe dn protoplasma de la-nf, qni, ayant acquis nne density plus graude que 

 la masse sous-jacente, se s^pare de celle-ci par un contour net et trancbi?. Elle est il I'ceuf ce que la membrane cellu- 

 laire est h, la cellule ; elle se forme de la meme manifere. 



According to this view the ovum is morphologically a cell, the vitelline membrane is the cell 

 wall. 



The origin and growth of the egg in Amphipods iOammarus locvsta) agrees quite closely with 

 what takes place in Alpheus and Homarus. According to Van Beneden and Bessels (60) the 

 young ova are at first protoplasmic cells, the nucleus of which becomes the germinal vesicle. The 

 ovarian egg is a cell without a membrane, and in the cell protoplasm refringent vesicles are devel- 

 oped which form the yolk elements. According to these authors the mature ovarian egg consists 

 of a viscous, finely granular, and contractile liquid, which represents the primitive cell j)rotoplasm 

 and holds in suspension the germinal vesicle, and, secondly, of nutritive yolk elements (called by 

 them deutoplasm because of secondary origin), which are also suspended in the protoplasm of the 

 egg. 



