18 THE YOUNG OF THE CKAYFISHES ASTACUS AND CAMBARUS 



The long auteuii:v remaiued for the most part low down amongst the gen- 

 eral mass and did not yet project up al)ove the level of the rounded backs; 

 they were, however, carried out in front and not, as in ('(iinhdiHS affiiiis, tucked 

 in between the legs. 



Fastened thus to the mother, the larva^ 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 kei)t 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 ])efore changing to the second stage and their fellows kept 

 in watei- 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 fiesh-color. 



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

 describe the details of the external form and aii|)endages 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 a way not 

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

 stalks are features of an embrj^o rather than of an active larva. The dark mass 

 seen in the tigure 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 colore.! liy the scat- 

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

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

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

 three maxillipeds are seen in ])art, tlie chehe are very long and heavy and the 

 fdur walking ](>gs are long and weak. The abdomen ])ears only fV)ur 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 larvte 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, llie chehe, 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 fi-ee to the water. 



The sanu> 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 tiiat the head-thorax though globoidal is 

 considerably elongated and does not liavc the swollen sides shown in Iluxlev's 



