768 NATURAL HISTOKY OF AQUATIC ANIMALS. 



numbers, from June 23 to late in August. They were most abundant in the early part of July, 

 and appeared in the greatest numbers on calm, sunny days. 



"Several Zoefe of this stage were observed to change directly to the megalops form. Shortly 

 before the change took place they were not quite as active as previously, but still continued to 

 swim about until they appeared to be seized by violent convulsions, and after a moment began to 

 wriggle rapidly out of the old zoea skin, and at once appeared in the full megalops form. The 

 new integument seems to stiffen at once, for in a very few moments after freeing itself from the 

 old skin the new Megalops was swimming about as actively as the oldest individuals. 



" In this megalops stage the animal begins to resemble the adult. The five pairs of cepha- 

 lothoracic legs are much like those of the adult, and the mouth-organs have assumed nearly their 

 final form. The eyes, however, are still enormous in size, the carapax is elongated and has a 

 slender rostrum and a long spine projecting from the cardiac region far over the posterior border, 

 and the abdomen is carried extended, and is furnished with powerful swimming-legs, as in the 

 Macroura. In color and habits they are quite similar to the later stage of the Zoe from which 

 they came; their motions appear, however, to be more regular and not so rapid, although they 

 swim with great facility. In this Megalops the dactyli of the posterior cephalothoracic legs are 

 styliform, and are each furnished at the tip with three peculiar setae of different lengths and with 

 strongly curved extremities, the longest one simple and about as long as the dactylus itself, while 

 the one next in length is armed along the inner side of the curved extremity with what appear to 

 be minute teeth, and the shortest one is again simple. 



"According to the observations made at Wood's Holl, the young of Cancer irroratm remain 

 in the Megalops stage only a very short time, and at the first molt change to a form very near 

 that of the adult. Notwithstanding this, they occurred in vast numbers, and were taken in the 

 towing-nets in greater quantities even than in the zoea stage. Their time of occurrence seemed 

 nearly simultaneous with that of the Zoeaj, and the two forms were almost always associated. The 

 exact time any particular individual remained in this stage was observed only a few times. One 

 full-grown Zoea obtained June 23, and place d in a vessel by itself, changed to a Megalops between 

 and 11.30 a. m. of June 24, and did not molt again till the forenoon of June 27, when it became 

 a young Crab of the form described farther on. Of the two other Zoese obtained at the same time, 

 and placed together in a dish, one changed to a Megalops between 9 and 11.30 a. m. of June 24, 

 the other during the following night; these both changed to Crabs during the night of June 26 

 and 27. 



"In the two or three instances in which the change from the Megalops to the young Crab was 

 actually observed, the Megalops sank to the bottom of the dish and remained quiet for some time 

 before the molting took place. The muscular movements seemed to be much less violent than in 

 the molting at the close of the zoea stage, and the little Crab worked himself out of the megalops 

 skin quite slowly. For a short time after their appearance the young Crabs were soft and inactive, 

 but the integument very soon stiffened, and in the course of two or three hours they acquired all 

 the pugnacity of the adult. They swam about with ease and were constantly attacking each 

 other and their companions in the earlier stages. Many of the deaths recorded in the above 

 memorandum were due to them, and on this account they were removed from the vessel at each 

 observation. In this early stage the young Crabs are quite different from the adult. The carapax 

 is about three millimeters long and slightly less in breadth. The front is much more prominent 

 than in the adult, but still has the same number of lobes and the same general form. The antero- 

 lateral margin ia much more longitudinal than in the adult, and is armed with the five normal 

 teeth, which are long and acute, and four very much smaller secondary teeth alternating with the 



