Fourth Legs Research Articles

The control of walking in the scorpion

1. Ablation of one walking leg from the scorpion does not diminish its ability to walk in a relatively stable and constant fashion (Fig. 1). Removal of one of the fourth legs results in maximal disturbance. 2. Subsequent to ablation of one walking leg, the posterior-anterior stepping sequence for alternate leg pairs is not absolute as it is for intact scorpions (Fig. 2, Fig. 3). However, the 4231 order remains the dominant gait. 3. Ablation of either leg 1 (Fig. 2) or leg 4 results in minimal reorganization of the remaining ipsilateral appendages. 4. Ablation of an internal leg, leg 3 for example (Fig. 3), results in ipsilateral phase shifts so that leg 2 and leg 1 step relatively later in the leg 4 cycle (Fig. 4). Such ipsilateral reorganization is proposed to contribute to overall stability. 5. Dual ablation preparations walk as predicated by the single ablation experiments. An intact tetrapod can be maintained as a functional unit and be used reciprocally with the two other legs (Fig. 6). It was also observed that the promotion durations were consistently shorter in the dual ablation preparations than in the intact scorpions (Fig. 7).

The occurrence, methods and significance of swimming in the Brachyura

Representatives of the following thirteen families of the Brachyura have either been observed to swim, or are suspected on morphological grounds of being capable of doing so: Raninidae, Homolidae, Calappidae, Corystidae, Cancridae, Portunidae, Xanthidae, Palicidae, Pinnotheridae, Grapsidae, Ocypodidae, Hymenosomatidae and Majidae. However, widespread swimming is confined to the Portunidae, Pinnotheridae, Grapsidae and Hymenosomatidae. For each species involved the natatory modifications and the techniques and functions of swimming are described as far as possible. The morphological adaptations for swimming are discussed, and the exceptional ability of the Portunidae is attributed to their having the fourth legs specialized solely for swimming, whereas the others use the same legs for both swimming and walking. The wide variety of swimming techniques is thought due to swimming having evolved on numerous separate occasions. The functions of swimming range from brief feeding or escape reactions to the maintenance of a wholly pelagic life.

罐詰タラバ蟹肉の部分に依る差違

The degree of blackening of the canned crab-meat and that of the blue-meat formation of the same were known to depend on the pH-value, and respective amount of volatile basic nitrogen, copper, iron, and hydrogen sulfide. As shown in Table 1, no difference was found in pH-valne, amount of volatile basic nitrogen, copper, total sulfur in the examined parts (protopodite, meropodite and propodite of the second to fourth legs), of the examind three individuals, that of iron being the same irrespective of the examined parts, but different in different individuals. On the other hand, the amount off hydrogen sulfide of the meat of protopodite was much more than that of meropodite and of propodite.

STUDIES ON THE SECONDARY SEXUAL CHARACTERS OF CRAYFISHES. IV. MALES WITH TWO SETS OF SUPERNUMERARY MALE CHARACTERS

In study number three of this series, males of Cambarus propinquusand of Cambarus virilis which bore supernumerary male characters were described. These supernumerary char acters were in the form of copulatory hooks ordinarily found only upon the third walking legs but in these cases present also upon the second or the fourth walking legs. In C. virilis the extra hooks were confined to the second walking legs. In C. propi@@quus the additional hooks were found upon either the second or the fourth walking legs. It was predicted that in C. propinquus, since either the second or the fourth walking legs might function in carrying the extra hooks, specimens might be found in which copulatory hooks would be present upon both the second and the fourth walking legs. During the summer of 1924 large collections were made from practically all the streams and some of the lakes of southeastern