THE BRITISH FOSSIL BRACHIOPODA. 303 



Lingula {Glottidid) pgramidata, by Morse, Brooks. 1 



Discina, sp., by Fritz Miiller. 



Kowalevsky has described and illustrated in great detail the development of Argiope 

 (Cistella) Neapolitana. He states that the eggs, after having detached themselves from 

 the ovary, fall into the general cavity of the body, enter the 

 oviducts by the funnel-shaped opening of these organs, and pass a ^^r^y^j^ 

 into the incubatory pouches, situated on the ventral lobe of the ^ 

 female individual, and where they are developed. He is of 

 opinion that the fecundation must, without doubt, be accom- 

 plished either during the passage of the egg along the oviduct, ' ~° 

 or in the general cavity. 2 ^ U . ^ _ 



First period. — From the commencement of the development 

 of the egg up to the moment when the larva fixes itself. 



In the less advanced state, Kowalevsky has observed that 

 the egg presents the aspect of a vesicle, of which the sides are 

 composed of little cylindrical cells surrounding a small cavity. 

 Soon after a portion of the blastoderm becomes invaginated 

 (Fig. A), the extremities of the gastrula approach each other 

 and leave between them only the place of an opening. At this 

 moment the embryo presents two layers of small cells ; one of 

 them is the outer layer of the blastoderm, the other the inner 

 layer; it is at the expense of this last that the middle segment 

 as well as all subsequent modifications are formed. 



In the next stage, the cavity divides itself into three lobes 

 (one median and two lateral), which communicate at the part the 

 nearest to the orifice. This orifice is connected with the median V l\\H«/|v// 



lobe by the means of a narrow canal, of which the walls a, b, c, Argjope Neapolitana 

 present two small prominences formed of small cells distinctly „ " kCmaevSiy - 



1 , . . ■'A. Egg after the invagination 



differentiated. Soon after the embryo divides itself transversely of a P art of the blastoderm: d, 



J cavity formed by the invagina- 



into two segments, the one upper and large (cephalic segment), tkm; «, orifice of the cavity; o, 



, , , -l/ii \ /t-.. exterior layer (upper) j u, interior 



tne other narrower and more conical (caudal segment) (Fig. B). layer. 



At this period the three lobes of the internal cavity separate two segments 1 ! ry ° ' 



themselves the one from the other and form three isolated in g of theSmti»Sr2y w« a 



cavities. The median cavity presents at its posterior portion so ^ephaiifsegme^ flES* 



great an approximation to its walls, that these last appear as £S^of taHff ^^ 



partition. At the anterior part the median cavity is surrounded, 



in addition to its own walls which are formed of cylindrical cells, like the envelopes of 



1 Chesapeake Zoological Laboratory, Scientific Results, Baltimore, 18/9. 



2 We have considered it desirable to translate here a portion of MM. Oehlert and Deniker's excellent 

 summary of Kowalevsky's memoir, as so few are able in this country to read the Russian language. 



