500 SUMMARY OF CURRENT RESEARCHES RELATING TO 



dermal cells. The testes are formed of hollow saccules, whicli consist 

 of an external connective tissue, and an internal epithelium ; as their 

 internal surfuce lias no peritoneal investment, tlie genital cells project 

 directly into the cavity of the sac. 



B. 3[crcschJioL-sJiil may bo regarded as a trochophorc provided with a 

 single, first, body-segment, and the cephalic ganglion. It is modified 

 by the i)ossessiun of certain characters (dorsal nerve-tube, gill-clefts, 

 cSjc), which bring it close to the Chordata. 



' Challeng"er ' Myzostomida.* — Dr. L. von Greeflf has publislied a sup- 

 plementary report based on the INIyzostomida found by Dr. P. 11. Car- 

 penter during the investigations of the Crinoids collected during the 

 voyage of H.JVl.S. ' Challenger ' ; seven new forms are described. 



Echinodermata. 



Development of Egg of Echinocardium cordatum.f — Herr A. 

 Fleisclimann has examined the early stages in the development of this 

 irregular Ecliinoid. The fertilized ovum is a homogeneous finely- 

 granular sphere of protoplasm inclosed in a vitelline membrane and a 

 rather thick gelatinous envelope. The first cleavage-plane is seen 

 about an hour and a half after fertilization, and segmentation is nearer 

 one pole than the other. The first plane appears first at the animal 

 pole, and later, extends to the vegetative, so that division is first com- 

 pleted at the animal pole. In consequence of the mode of appearance 

 of the second plane there is, for a short time, a three-celled phase of 

 cleavage. The cleavage-cavity next begins to appear, and has at first 

 a somewhat tubular form, but, owing to the closer approximation of the 

 cells of the uj^per (animal) pole, the cavity takes the form of a trun- 

 cated cone. 



From the very beginning of cleavage the egg loses more and more its 

 distinctly spherical form, and the four cleavage " spheres " are drawn 

 out. The details of cleavage are given, but the result attained is that 

 differences in cleavage have no anatomical or phylogenctic significance. 



Renal Organ of Echinoids.:|: — Herren P. and F. Sarasin offer a 

 suggestion as to the function of the brownish organ which accompanies 

 the stone-canal of Echiuoids, and has had such different uses assigned to 

 it. In Asthenosoma the organ is for its whole length traversed by a 

 large cavity ; from this there are given off a number of large glandular 

 lobes with narrow liunina. The glandular tubes opening into the chief 

 cavity contain large clear vesicular cells, which, in a striking manner, 

 call to mind the renal cells of Molluscs. The tubes are imbedded in a 

 stroma of connective tissue, in the smaller or larger meshes of which 

 the nutrient hoamolymph circulates. Fine canals lined by regular 

 epithelium are given off' from the large glandular lobules, and then make 

 their way towards the periphery, and after a more or less coiled course, 

 pass into larger spaces, which open on the surface of the organ by small 

 orifices into the coelom ; these during life are well ciliated. The authors 

 believe that these infundibular openings of the renal canals correspond 

 to the ciliated infundibula of certain Holothurians, and they believe 

 that they are right in calling them nephrostomata. The well-known 



♦ Reports of H.M.S. ' Challenger,' Myzostomida (ii.), Ix. (1887) 16 pp., '1 pis. 

 t Zeitschr. f. Wiss. Zool., xlvi. (1888) pp. 131-42 (1 pi.). 

 % Zool. Aiizcig., xi. (1888) pp. 217-8. 



