50 SUMMARY OF CURRENT RESEARCHES RELATING TO 



from one anotlier by tlie reddisli colour of the ovaries, and the white- 

 ness of the testes. They lie in the coils of the enteric canal, and are 

 in both cases provided with a pair of ducts, which open to the exterior 

 between the seventh and eighth segments. No directive corpuscles 

 could be observed in the mature unfertilized ova. The ducts of 

 Sternaspis appear to be special structures and not modified segmental 

 organs. The cleavage of the egg appears to take place rapidly, inas- 

 much as after sixteen hours there are seen ciliated embryos ; the 

 whole of the body, with the exception of the hinder end, is covered with 

 very fine cilia, and a tuft of longer ones is seen at the anterior end. 

 The embryo gradually grows narrower posteriorly, and the porous 

 cuticle corresponds exactly to the yolk-membrane, which seems to 

 grow with the body. The anterior end becomes divided into three 

 lobes, of which the median is the largest. At this period the endo- 

 derm fills up the whole of the tube formed by the ectoderm, and, so, 

 exactly resembles the Planula of the Hydromedusce. After forty-eight 

 hours the larvfe are twice as large, have lost all their cilia, and have 

 the form of a non-ciliated Turbellarian without mouth or anus. A 

 new cuticle, which has very much the appearance of a former one, is 

 developed over the whole of the body ; the ectodermal cells become 

 much more distinct, and those of the endoderm begin to indicate the 

 foi'mation of the enteric tube. At the hinder end of the body the two 

 layers are now separated and the intermediate space is occupied with 

 spindle-shaped nucleated elements, which perhaps owe their origin to 

 the endoderm. After five days the cephalic lobes appear, and the 

 mesoderm is found to have given rise to muscle-cells. On the sixth 

 day, when the observations ceased, the excretory canals began to appear. 



In conclusion, the author thinks that there are four natural orders 

 of the class Annelides : (1) Hirudinea ; (2) OUrjocliceta ; (3) Polychceta ; 

 and (4) Gephyrea. In a phylogenetic table he shows that he would 

 derive the first two from the Discodrilida, and the other two from 

 Sternaspis ; the Discodrilida form an offshoot from the Oligochgete 

 stem which descends into the Amedullata, which, with Siernaspis, have 

 their common origin in the Turbellaria, which, for their part, are 

 derived from the Coelenterata. The Polygordiidae (Acluvta Balfour) 

 seem to Dr. Vejdovsky to form a group of the Polychaeta. 



The author believes that the larvae of the Chaetopods and Gephyrea 

 are formed on the same type, and that in Echiurus there is a true 

 segmentation of the body. 



Hamingia glacialis. * — In his detailed account of this new 

 Echiurid.t Dr. E. Horst points out that the digestive tract presents a 

 number of coils, that the mouth forms an elongated cleft, and that the 

 conical pharynx is separated by a constriction from the oesophagus ; 

 this latter is somewhat pushed to the right side owing to the great 

 development of the uterus. The vascular system possesses a ventral 

 vessel which accompanies the ventral end, along its whole length ; a 

 dorsal vessel which does not extend over more than half of the body, 



* Niederl. Arch. f. Zool., Suppl. Bd. i. (1881) 1st art., 12 pp. (1 pi.), 

 t See this Journal, i. (1881) p. 891. 



