Breeding Habits.

There is good reason to believe that Amphipholis squamata, unlike most other ophiuroids, breeds throughout the year, a constant stream of eggs being produced one by one and fertilised. Thus at any time of year embryos may be obtained at various stages of development, though the earliest stages are of course very rare, owing to the comparative rapidity of the first cleavages, and the fact that only one egg is formed at a time. The difficulties in obtaining information on these early cleavages are thus closely comparable to those encountered in the mammalia.

Garstang recorded that A. squamata breeds at Plymouth, England, from May to September. However, specimens forwarded to me from Plymouth in February, 1940, during an exceptionally cold winter, proved to be carrying embryos at various stages, so that there is no reason to believe that the species has a restricted breeding period at that locality. Specimens from the Firth of Clyde area indicate that breeding continues uninterruptedly throughout the year on the West coast of Scotland. In the Forth area, on the other hand, somewhat different results were obtained, probably as a result of the more severe winter conditions of the North Sea. Thus, from January to March, 1940, no specimens at all could be obtained, and it was not till June of that year that the species was again common. However, whenever specimens have been obtainable in the Forth area, they have always been pregnant, so that it would seem that so long as the weather conditions are suitable for the life of the adults, these will breed.

In Forth specimens it is unusual to find more than five of the ten bursae pregnant at any one time, and each bursa seldom contains more than one embryo. In specimens from the Clyde, on the other hand, not only are the adults themselves much larger than examples from the Forth, but they also carry a greater number of embryos, and the latter are often much more advanced. Thus it seems that on the milder Atlantic coast the embryos are carried for a longer period before being born. This is a peculiar fact, as it is more usual for brood protection to be more highly developed in unfavourable conditions. In one particularly prolific specimen, forwarded from Millport, the following embryos were extracted: in one bursa were an embryo having 8–9 arm-segments, an embryo with 3–4 arm-segments, and an embryo at the “pentagon” stage; in another bursa were two embryos, one with 10–12 arm-segments, and one with 3–4 arm-segments; in a third bursa were two embryos with 3–4 arm-segments; one bursa was empty; and the remaining six bursae each contained one embryo, ranging in development from 3–10 arm-segments.