OF DENISON UNIVERSITY. I9 



The accessory branch of the second antenna, with its forceps, has be- . 

 come large. Now the hypodermic contents of the antennules with- 

 draw from its shell and compact themselves into the mature form, de- 

 veloping, at the same time, sensory rods in their substance. The con- 

 tents of the labrum fall away from the walls and gather into a lobe-like 

 body. Feet have formed, and a single-chambered heart is actively 

 pulsating. The future shell may now be seen under the larval cover- 

 ing, connected only with the back over the segments bearing gnathites, 

 and hanging free about the edges. When the moult is affected the 

 labrum falls within the valves, carrying with it the small tactile anten- 

 nules, which hang pendant by a slender stalk. The frontal promi- 

 nence, however, is elongated, forming the beak. The larva is now a 

 diminutive of the adult. In its future development the form elongates 

 and finally again becomes rounded and assumes the familiar appear- 

 ance. The branches from the stomach fill the front of the head with 

 so-called liver-lobes. The compound eye becomes perfected, while 

 the nauplius eye is covered by filaments charged with some unknown 

 sensory function. The heart becomes multi-chambered and the geni- 

 tal organs appear. For a figure of a young Limnetes, see Types of 

 Animal Life^ etc., by the author; for figures of the adult and a discus- 

 sion of relationships, see Packard's '' Monograph of the Phyllopod 

 Crustacea of America"; U. S. Geol. Surv. of Teri-. 187S, Part I. 

 Farther details may be gathered from the plates. It is a matter of 

 regret that Grube's work on the development of the European Lim- 

 netes brachyura was not accessable to me during the period which was 

 covered by this paper. My recollection is, however, that the pro- 

 cesses are, in the main, identical, but that Grube fails to identify all 

 the organs of the embryo. 



B. Post-e7nhryonic Development oj Chirocephahis. 



The species studied is assumed to be the common C. hol77iani^ Ryder, 

 although the oldest male seen differed in several particular from the 

 description of that species. One must imagine a fish-like, transparent 

 animal, about one-half inch long, balancing itself in the water by the 

 movement of eleven pairs of lamellate swimming feet. The colors 

 are brilliant and do not interfere with an almost perfect transparency of 

 the body. 



The earliest stage seen is that figured on Plate V, Fig. i. The 

 animal is at that period .93 mm. long and the antennae measure about 



