455 



wissen Entwickelungspliasen durch innigere Aneinanderlagerung und 

 gegenseitige Abflachung der Zellen zeitweise verändert wird. 



Der M u n d p o 1 der jungen Hydra entspricht dem vegetativen 

 Pole des Eies. 



Graz, am 1. August ISSO. 



5. Preliminary Abstract of Observations upon the Early Stages of some 

 Polychaetous Annelides. 



By E. B. Wilson, Fellow in Biology, Johns Hopkins University, 



The following is a brief summary of some observations on the de- 

 velopment of the marine Annelides, and is published as preliminary to 

 a more extended illustrated paper upon the subject. Notwithstanding 

 some excellent work in this direction a very wide field for research is 

 unexplored; and the early stages, the segmentation and formation of 

 the germinal layers, are very imperfectly known. During this and the 

 proceding summer I have had an opportunity at the Chesapeake Zoo- 

 logical Laboratory of studying the early stages of a few forms, the re- 

 sults of which studies are here in part summarised. 



1) Glymenella torquata (Leidy) Yerrill. The eggs are slightly oval, 

 of considerable size, with granular opaqu eprotoplasm and a rather thin 

 apparently homogeneous enclosing membrane which is directly con- 

 verted into the cuticle of the larva. They are several hundred in 

 number and are embedded in masses of firm transparent jelly issuing 

 from the mouths of the tubes secreted by the worms. The segmentation 

 is closely similar to that of the Oligochaetous genera Euaxes and Tu- 

 bifex as described by K o w a 1 e v s k y ; and it is , if the account of 

 Claparède and Metschnikoff is correct, somewhat unlike that of 

 other Polychaeta. No polar globules of any constant position were ob- 

 served. The first cleavage divides the egg into two unequal spherules. 

 The second divides the smaller of these into two equal parts and the 

 larger into two unequal parts. The third cleavage separates from these 

 four primary blastomeres four much smaller ones (micromeres) at one 

 pole of the eg^. The latter soon become so displaced as to alternate 

 with the former (macromeres) . 



The micromeres increase in number by sub- division and receive 

 accessions from the division of the macromeres, which they grow 

 around and include. Two large spherules, derived from the larger of 

 the two primary blastomeres, are visible up to a late stage at the poste- 

 rior end of the embryo. At first at the surface, they are subsequently 

 grown over by the ectoderm and disappear. I cannot state their rela- 

 tion to the germ-bands, a question which must be reserved for study by 

 means of sections. The mouth appears on the ventral side nearly oppo- 

 site to the point where the first four micromeres were formed. The 



