ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
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recall the modified limbs of adult Promise . The Promise have been 
divided into two groups ; those which have two pairs of modified limbs 
and those which have only one. Dicranodromia in the adult condition 
belongs to the former of these two groups, but in the embryonic 
stage it exhibits the more primitive type, in which only one pair of 
limbs was modified. 
Segmentation of Ovum in Terrestrial Isopods.* — Prof. J. Playfair 
McMurrich has come to very different conclusions from those to which 
Roule was led by his investigation of Porcellio scaber. The author, who 
has followed step by step the segmentation of several Isopods, is able to 
state with certainty that in none of these forms does a telolecithal 
segmentation occur, but in all it is of the same type as the typically 
centrolecithal Porcellio and Armadillidium. Immediately after fertiliza- 
tion the nucleus occupies practically the centre of the egg, where it lies 
imbedded in a mass of protoplasm, from which delicate processes radiate 
off into the yolk. Enclosing the yolk is a delicate layer of protoplasm 
entirely destitute of nuclei, and probably, to judge from what occurs in 
the egg of Jaera, united with the central nucleated mass by a reticulum 
of protoplasm, the yolk being distributed in the meshes of this reticulum. 
The full details as to segmentation and certain interesting phenomena 
which accompany it will be given in a paper which is promised us. 
The author confines himself at present to pointing out that the segmen- 
tation of Porcellio and Armadillidium is identical with that of Asellus. 
These statements are at utter variance with the observations recorded 
by Roule, but, as the author observes, they may be readily verified by 
the use of proper methods. He suggests that Roule has mistaken a 
stage at which the nuclei had already reached the surface for the stage 
immediately succeeding fertilisation. This failure to perceive the true 
significance of the structures in question is thought to be due to the 
imperfect methods which the French naturalist adopted. 
Pelagic Crustacea in Green Lake, Wisconsin.! — Mr. C. D. Marsh 
reports that Green Lake is the deepest body of water in the State of 
Wisconsin, having a maximum depth of about 60 metres. It has, there- 
fore, not only the littoral and pelagic faunas of shallower bodies of 
water, but also the true abyssal fauna which is characteristic of the 
deeper lakes. In these deeper waters there are found 15 species of 
Crustacea. Of these 12 may be considered as belonging peculiarly to 
the deep water fauna. Most of them can be captured in very large 
numbers at night by means of the skimming net. The author expected 
to find the three regions characteristic of the deep sea — the pelagic, the 
intermediate, and the abyssal. He was rather disappointed therefore 
when he found material in his dredge from all depths. The species 
found in greatest numbers is Piaptomus minutus. More than one-half of 
the individuals of this species are found within 10 metres of the surface, 
and from that point to the bottom the numbers steadily decrease. 
Paphnella is more exclusively pelagic, and Ppischura is still more dis- 
tinctly pelagic, 81 per cent, being found in the first 10 metres, and 3*3 
per cent, in the last 10. Pontoporeia and My sis live at the bottom, and 
* Zool. Anzeig., xviii. (1895) pp. 109-11. 
f Amer. Natural., xxviii. (1894) pp. 807-9. 
