1887.] NATURAL SCIENCES OF PHILADELPHIA. 299 



the outer mantle was unusually thiu and soft as if newly formed, 

 while the exuviffi were stiff and elastic. 



The "Inner Mantle" presents an ectodermal and an entodermal 

 cellular layer, which are separated by a hyaline connective basis 

 substance, of varying thickness, in which lie buried the viscera and 

 the muscular bands, and through Avhich a net-work of blood sinuses 

 burrow in all directions. 



The ectoderm consists of a single layer, of pavement epithelium, 

 made up of polygonal, usually hexagonal cells (Plate xiii, figs. 1, 2), 

 in which the protoplasm with its oval, often slightly bowed nucleus 

 occupies the central portion ; the remainder of the cell appearing 

 empty and transparent, and the boundaries between neighboring cells 

 being very poorly defined. These cells lie directly upon the basis 

 substance of the inner mantle, and are on their outer surftice in 

 contact with the cuticle or outer mantle. 



I have nowhere in the ectoderm of Salpa been able to find such 

 large j)avement cells, containing a protoplasmic reticulum extending 

 out from a centre plasma-mass as Uljanin^ and Grobben^ described 

 in the larvae of Doliolum; but in several young specimens I find a 

 layer of epithelial cells, lining the cavity containing the elseoblast 

 which present an appearance corresponding in almost every partic- 

 ular to those described by IJljanin. The plasma of these cells is 

 mostly collected into a central mass from which go out i:)rocesses, 

 anastamosing freely and connecting it with a thin, less granular lay- 

 er at the periphery. The nuclei are oval in form and sometimes lie 

 to one side of the central mass. Not having living specimens at 

 hand, I was unable to ascertain anything in regard to the granular 

 streaming in the protoplasmic network or the retraction of processes 

 and the extension of others by the central mass as described by 

 Uljauin. These cells lining the elteoblastic cavity are several times 

 larger than the cells of the ectoderm covering the body, but they 

 are similar in structure, and are probably larger because younger, 

 since Uljanin found several undergoing fission. At the two openings 

 of the body, branchial and cloacal, the ectoderm passes over into the 

 entoderm or layer of cells lining the inner mantle ; these corresjiond 

 almost exactly with those of the ectoderm, except that the cells are 

 usually from one third to one half smaller. They vary both in 



1 1. c. p. 13. 



2 C. Giobben : Doliolum und sein Generations wechsel, Arbeiten ties zo 

 olog. Institutes zu Wien. Bd. IV, II ft. 2. 



