No. 396.] REVIEWS OF RECENT LITERATURE. 979 
sity (photopathic reaction), and is not, as far as is known, a color 
response (chromopathy). Gür 
Embryology of the Cladoceran Penilia. — The development of 
Penilia has been studied by M. T. Sudler.! The four to six oval 
eggs of a single laying are usually so placed in the brood sac of the 
female that their long axes are very nearly parallel to that of the 
female. The long axis of the egg corresponds to that of the future 
embryo, and the end of the embryo pointed forward in the brood sac 
becomes the head. The segmentation of Penilia is total and remains 
so throughout in strong contrast to that in most other Crustacea. As 
in Nereis, the first cleavage plane is transverse to the chief axis of 
the future embryo ; the second is in the sagittal plane; and the third 
is at right angles to both previous planes ; the fourth is parallel to 
the first; and from the fifth on, no clear characterization can be 
made. Gastrulation takes place in definite relation to the maternal 
body, ż.e., at what may be described as the outer posterior corner of 
the embryo. The mesoderm originates from either side of the mid- 
ventral line, and in a way that prevents it from being clearly dis- 
tinguished from the entoderm for some time. The gastrula mouth 
closes in the region afterwards occupied by the anus. The order of 
appearance of the appendages is open to some variation, but is 
usually as follows: second antenna, first antenna, mandible, first 
maxilla, second maxilla, thoracic appendages in sequence from the 
anterior end. Organogeny is briefly dealt with. The reproductive 
organs cannot be traced to a single cell, as in Moina according to 
Grobben. On the whole, Penilia gives evidence of being a highly 
specialized rather than a primitive cladoceran. GHP. 
Artificial Parthenogenesis in the Sea Urchin. — Observations on 
the influence that various dissolved substances have on living muscle 
and on the fertilized and unfertilized eggs of marine animals have 
led Loeb? to suspect that the reason unfertilized eggs do not 
develop is not only because of lack of the spermatozoan, but also 
because of the constitution of the sea water. The addition of mag- 
nesium chloride to sea water (5000 12n MgCl, in 5000 cc. of sea 
1 Sudler, M. T. The Development of Penilia schmackeri Richard, Proc. Bos- 
ton Soc. Nat. Hist., vol. 29, pp. 109-131, 3 plates. October, 1899. 
2 Loeb, J. On the Nature of the Process of Fertilization and the Artificial 
Production of Normal Larvz (Plutei) from Unfertilized Eggs of the Sea Urchin, 
Amer. Journ. Physiol., vol. iii, pp. 135-138. October, 1 
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