RHIZOPQDA. 7 



In size it may vary from .036 mm. to .260 mm. in length. The nucleus and contractile 

 vesicle are conspicuous in the posterior portion. In all the shelled forms the food is 

 taken in at the mouth of the shell, and the d6bris is ejected at the base of the pseudo- 

 podia. 



Okdeb II. — RADIOLARIA. 



When Prof. Huxley was engaged in studying the fauna of the sea on. board H. M. S. 

 "Rattlesnake," about thirty years ago (1851), he found floating upon the seas, whether 

 tropical or extra^tropical, some peculiar gelatinous bodies to which he gave the name 

 Thalassicolla, signifying sea-jelly. These were among the most common objects from 

 the tow-net, and their extreme simplicity of structure made it very difiicult to classify 

 them in the animal kingdom. Imagine a colorless, transparent gelatinous mass, spheri- 

 cal, elUptical, or elongated in form or contracted like an hour-glass in one or more 

 places, varying in size from a mere spec up to 

 an inch in length, without contractility or power 

 of motion, but floating passively upon the 

 water : such is Thalassicolla, Fig. 4. 



Two species were described by Prof. Hux- 

 ley in his account of these organisms. One 

 of them, T. punctata, is characterized by an 

 appearance of dots scattered about near the 

 internal surface of the thick, gelatinous crust 

 which may surround either a single large 

 cavity or a number of clear spaces closely 

 aggi-egated. The appearance of dots is pro- 

 duced by nucleated cells, which are imbedded 

 in, and held together by, the gelatinous crust. 

 The cells are about -^^-^ or -^^-^ of an inch in 

 diameter, and are covered with a thin mem- 

 brane. Surrounding the cells or diffused through the connecting substance are minute 

 bright-yellow corpuscles. The cells may also be enclosed within a framework of crystals 

 or spicules resembling the spicules of a sponge. 



T. nucleata is a spherical mass, characterized by a blackish central portion, around 

 which is a zone of vacuoles or clear spaces with yellow cells and dark granules, which 

 is in turn surrounded by the outer, clear, gelatinous substance. The dark central por- 

 tion is a vesicle with granular contents and a firm, colored membrane. From the dark 

 centre delicate branching fibrils radiate and anastomose through the zone of vacuoles, 

 extending almost to the periphery of the sphere. 



Thalassicolla may be regarded as a type of the Radiolarian structure. The Radio- 

 laria are characterized by having a central nucleated portion surrounded by an outer 

 peripheral mass, from which it is separated by a porous, more or less resisting mem- 

 brane known as the capsule. Both the mass within the capsule and the sarcode with- 

 out consist of very soft and contractile protoplasm, in which are imbedded colored 

 globules, vacuoles, and perhaps other structures. Most Radiolaria have a skeletal frame- 

 work of silicious spicules, or beautifuUy-designed structures, which may be found either 

 within or without the capsule. The silicious framework of these minute organisms, 



Fig. 4. — Thalassicolla morum. Greatly enlarged. 



