396 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



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

 Nassau, Palinurus begins to spawn in June. 



(d) Cknnpiii-inon. Ishikawa describes very fully the ovaries and ovigenesis of the prawn At- 

 i/t'/il///i-n miiqircxm 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 au 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 fluid by which the eggs are attached to the swimmerets, yet this point needs cornfir- 

 ination. 



The chorion was found in the ovarian egg of Pagurus by Mayer (.'9), who says: 



Dan EiiTstoc.ksei von Pa^'mis j H t in dor crsten Zeit seines Bestekens eine eehte Zelle mit Protoplasina, Kern und 

 Kern-Korperchen. Spiiter findeteine Einlagerung von Deutoplasuia und die Bilduug einer Hiille aus Cbitiu statt. 

 Eudlieli \vird iler Kern unsiulitbar ; das Ei wtcllt danu eine Cytode vor. 



Das t'erlige 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 flumatilis) is inclosed by ; 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 (2G) merely states that '" a structureless vitellme 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 

 choriou is clearly the secretion product of the ovisac. 



In C run ;/<> it nili/aris Kingslcy (ol) finds that the late ovarian ova resemble the newly laid 

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



Lud wig'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 eyg membranes, those which are derived from the protoplasm of the egg 

 itself or from its follicle cells, and srrt>niltiri/ <//// mcmbrn-nes, those formed by the wall of the oviduct 

 or otherwise. Balfour, following Van Beueden, 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 category of secondary structures would fall also those secreted by special 

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

 winter eggs of Daphnia and Tardigi ada, which is due to a moult or direct separation 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 (GO), thus define it: 



Nous entendous la membrane vitelline dans le sens oil M. (.'lapan-de fa si nettement ddnnie dans son travail sur 

 les vrrs Ne'matodes : C'est la couclie exterue ilu protoplasma de 1'u'iif, qni, ayant acqnis uno deusit.6 plus grande qne 

 la masse sons-jaconte, se se'pare de cellc-ci par un contour net et tranche'. Elle est iX IVeufce que la membrane cellu- 

 laire ost ;\ la cellule ; elle se forme de la meme maniere. 



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 Arnphipods (Gammarus locusta) agrees quite closely with 

 what takes place in Alpheus and Ilomarus. According to Van Beneden and Bessels (GO) 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 protoplasm 

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

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

 egg. 



