18 THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBAKUS 



The long antennae remained for the most part low down amongst the gen- 

 eral mass and did not yet project up above the level of the rounded backs ; 

 they were, however, carried out in front and not, as in Cambarus affinis, tucked 

 in between the legs. 



Fastened thus to the mother, the larva 1 remained some days and then cast- 

 ing off their shells passed into a second larval stage which also lived upon the 

 mother. In one female kept in running water at 17 C., the duration of the first 

 larval stage was only four days, but some young of another female which 

 were kept suspended from strings hanging in water in a warm room remained 

 five to seven days before changing to the second stage and their fellows kept 

 in water at 14 C. remained eleven to thirteen days in the first stage. Dur- 

 ing this long existence in the first larval stage the only change noted was a slight 

 darkening of the color which, owing to the scattering of bright red, branching, 

 pigment cells on a white background appeared to the naked eye flesh-color. 



Before considering the transition from the first to the second stages we will 

 describe the details of the external form and appendages of the first larva. 



A side view of the living larva (fig. 3), suggests embryonic incompleteness 

 in that the antenna', abdomen, and limbs are carried downward in n way not 

 adapted to locomotion, while the globose cephalothorax and large eyes with short 

 stalks are features of an embryo rather than of an active larva. The dark mass 

 seen in the figure was the still conspicuous red yolk mass which from the dorsal 

 view (fig. 4), was balanced right and left in the anterior half of the cephalo- 

 thorax. In life the larva was translucent yet brilliantly colored by the scat- 

 tered pigment cells indicated in black in the figures and which were absent only 

 from the terminal filaments of the antennas and from most of the segments of 

 the legs. In the side view the first and second antennae are conspicuous, the 

 three maxillipeds are seen in part, the chelae are very long and heavy and the 

 four walking legs are long and weak. The abdomen bears only four pairs of 

 pleopods and these are small, weak, and bifid. The first and sixth pleopods are 

 not seen and the abdomen ends in a simple telson in place of the locomotor fan 

 of the later larvae and adults. The larva is evidently very defective in locomotor 

 apparatus, has its sensory organs not perfected, and is specialized in its strong 

 clinging organs, the chelae, and in its large digestive apparatus for utilization 

 of the stored-up yolk. It is still essentially embryo-like in structure and in 

 mode of dependent life, but is exposed free to the water. 



The same general features are shown in the dorsal view (fig. 4), which 

 shows the split-open egg capsule and its stalk, connected by a slender thread 

 to the telson of the larva, a "telson- thread" that is fast at one end to the 

 peculiar fan-like telson of the larva and at the other end to the inside of the 

 ruptured egg capsule. It will be noted that the head-thorax though globoidal is 

 considerably elongated and does not have the swollen sides shown in Huxley's 



