506 SUMMARY OP CURRENT RESEARCHES RELATING TO 



Heterogeny of Daphnia.*— C. L. Herrick, in the course of re- 

 searches upon the development of Daphnia Schaefferi ( = magna), 

 observed several interesting facts. 



The embryo, before leaving the egg, in both summer and winter 

 forms, is furnished with palpi on the base of the second antennae, and 

 a long appendage from the dorsal region of the shell. The former, 

 though quite large in the embryo, is later nearly atrophied, remaining 

 durino' life, however, as a wart-like process with two rather small 

 spines. The latter is curved beneath the body, lying between the 

 valves of the shell. After the escape of the animal from the egg this 

 organ becomes the dorsal spine, and seems to serve as an aid to the 

 complete moulting of the walls of the brood-cavity, with the first 

 development of which the spine seems also to stand in intimate 

 relation. 



It is worthy of remark that not only the mature animal, after long 

 confinement in aquaria, becomes smaller and stouter, and in other 

 peculiarities resembles the smaller spined species of Daphnia, but 

 that the young retain the dorsal spine and the shorter form till in a 

 sexually mature condition, when in confinement. This fact, and the 

 discovery of Dr. Birge, that the spine upon the head of another 

 species of Daphnia is also an embryonic organ, serve to call attention 

 to the systematic position of this genus. It would therefore appear 

 that the species Schaefferi is the culmination of a cycle of forms, 

 among which are to be counted more or fewer of the species described 

 as distinct. 



Daphnia thus furnishes another example of so-called " Heterogeny." 



Notodelphyidae.| — W. Giesbrecht describes the female repro- 

 ductive organs of these parasitic Copepoda. The ovarian tubes are 

 completely differentiated before the last ecdysis, when they present 

 the following features ; there is a structureless tunica propria lined 

 by a simple epithelium, the cells of which are as broad as high. As 

 changes occur, this epithelium becomes separated off from the wall of 

 the tube ; the process commences at the anterior end, and gradually 

 passes backwards, so that in a series of sections the anterior ones are 

 filled with the separated cells, while the lumen of the hinder ones is 

 still open and the wall invested by epithelium ; the cells do not break 

 off separately but in longitudinal rows. When this process has come 

 to an end, the walls of the tube are formed by a distinct membrane, 

 which is lined by a layer of protoplasm ; at first the nuclei in this 

 latter are at some distance from one another, but they soon come 

 to form groups of two to six. The tube, therefore, first had the 

 function of a germ-producer, and may be called the ovary, while, 

 later, it serves as an oviduct, and affords nutriment to the growing 

 ovarian cells. Owing to their coming off in longitudinal rows, the 

 ova now lying in the tube are arranged in cords of a cylindrical form, 

 each of which may have as many as one hundred eggs ; there is no 

 investing membrane to these ovarian cords. A little later the 



* Zool. Anzeig., v. (1882) pp. 234-5. 



t MT. Zool. Stat. Neapel, iii. (1882) pp. 293-372 (3 pis.). 



