1892.] Embryology. 75 



when kept in aquaria with ulva, which they eat. The male enters the 

 tube only to fertilize the eggs as they are laid. From the tubes the 

 eggs may be removed with care from holes cut in the side ; but the 

 female must not be disturbed, as the undulatory movements of its h<>d\ 

 within the tube are necessary in supplying the eggs with fresh water. 



When no male is present the females abandon the tubes ami lay the 

 eggs at random in the water, where they do not develop. 



No time limits can be set to the processes of development, as tin v 

 vary so exceedingly at different temperatures. It is interesting to note 

 that the author finds the Winter season very unfavorable, since a large 

 proportion of the eggs then develop abnormally in the laboratory, but 

 not outside. This would seem another illustration of the advantage 

 derived from a climate in which air and water are of about the same 

 temperature. At Messina the egg^ are laid, in aquaria, between eleven 

 and twelve in the morning regularly, this being a decided exception to 

 the many cases in which the night time is the laying period. 



In the investigation both surface views and sections were made use 

 of, the former either alive or stained in Kleinenberg's hematoxylin 

 after hardening in picro-sulphuric, while the section material was 

 hardened in Fol's modification of Flemming's fluid. 



The author's summary of results obtained is about as follows: Cleav- 

 age is total and unequal ; four blastomeres bud off four micromeres 

 called encephaloblasts, as they give rise to the cephalic ganglia and all 

 the sense organs of the head. The largest of the four micromeres 

 buds off two large cells called somatoblasts, as they form all the body 

 except the mid gut and the epidermis. The three oth 

 equal in size, bud off each two small cells, and these , 

 take no part in the formation of organs, but merely form the epider- 

 mis and the larval prototroch. 



The embryo arises from two quite separate masses, the one, the trunk 

 arising from the two somatoblasts, the other, the head, formed by the 

 four encephaloblasts. These two elements subsequently unite. The 

 embryo is hatched with three pairs of functional parapodia, the devel- 

 opment being thus direct. 



Without the aid of the author's figures it is difficult to explain 

 many of the points of interest in the paper, not all of which are 

 included in the above summary. 



The large amount of yolk present remains in four masses, the mic- 

 romeres, which are epibolically overgrown by a very thin layer of 

 nucleated protoplasm furnished by the cells budded off from the mic- 



