ECONOMY OF THE DAPHNIA. 173 



able personally to make any satisfactory observations. Sir John 

 Lubbock says they are produced from two determinate ovarian 

 masses in the lower part of the ovary, one on each side ; thus, 

 there are never more than two to fill the two ampullae of the 

 ephippium. Their development in the ovary is not accompanied 

 by the presence of oil-globules, as is the case with the agamic 

 eggs, and they are much darker in colour (see Figs. 13 and 6). 

 Sir John Lubbock has witnessed the passing of the yelk-mass from 

 the ovaries into the receptacle, where they are received into a 

 specialised portion indurated by a dense cellular growth (Fig. 28), 

 which speedily closes upon them. They are then cast off with the 

 next moult, secure in their covering against the adverse influence 

 of drought, or, as some say, of the winter's cold, but the former 

 appears to me the more probable hypothesis, inasmuch as I have 

 found the ephippia produced in the greatest abundance in the 

 months of May and June, when the concurrent abundance of 

 males gives weight to the beHef that the eggs so produced are true 

 sexual products. The position of the testis in the male cor- 

 responds to that of the ovary in the female, and is shewn at /, 

 Fig. I. 



EXPLANATION OF PLATES XVIII. and XIX. 



Fig. 1. — Male Daphnia psittacea, showing sa. , large superior antennse ; 

 1, first pair of feet, with hook and filament ; md. , mandible ; 

 t., testis. 

 ,, 2.— Female D. psittacea: h., the hood ; s g,, the shell-gland ;//., 

 lines of fission of the carapace; ejjJi., ephippium with two 

 eggs. 



ii 3. — Front view of head of D. vetula : cce., the coeca ; Ir., the 



labrum ; x x., jointed organs at base of the great antennse, 



the rest as before. 

 ,, 4. — Female D. psittacea, showing agamic eggs in brood receptacle : 



mmm., muscles of antennse j/^?., dark mass of food particles ; 



ht., heart ; |js., pericardial sinus ; 1, 2, 3, 4, 5, pouches of 



five pairs of feet ; a. , anus ; r. , rectum ; pr. , process of 



abdomen retaining eggs. 

 ,, 5. — Portion of shell-gland of D. pulex. 

 ,, 6. — Ephippial egg of D. psittacea. 

 ,, 7. — Diagram, section of carapace, showing double wall with blood 



globules between. 

 ,, 8. — Ditto, showing ephippium closing upon the egg. 



