154 BULLETIN OP THE BUREAU OF FISHERIES 



Breeding habits. — The spawning of Meganyctiphanes has not actually been 

 observed either in American or European waters, but it seems certain that this 

 genus either does not carry its eggs with it at all after they are extruded, as some 

 other euphausiids do, or that it nurses them only for a brief period at most, both 

 because ovigerous females have never been seen, so far as I can learn 82 (Holt and 

 Tattersall, 1905), and because eggs probably ascribable to this species have been 

 found free floating in the one-celled stage by Sars (1898) and by Lebour (1924a). 

 It is true that the eggs of Meganyctiphanes have not been identified with 

 absolute certainty from among the plankton. Sars (1898), however, thought it 

 probable that at least some of the euphausiid eggs 83 about 0.7 to 0.8 millimeter in 

 diameter, which he found in Christiania Fjord where Meganyctiphanes is plentiful, 

 had that parentage. Similar eggs had already been recorded from the Clyde area, 

 a center of abundance for Meganyctiphanes, by Brook and Hoyle (1888). Holt 

 and Tattersall (1905, p. 103), too, have assigned to this genus certain loose ova 

 found side by side with Meganyctiphanes and occasionally even clasped between 

 its thoracic legs, among various articles of prey, though without describing the 

 dimensions or appearance of the eggs in question. Lebour (1924) has recently 

 ascribed to this same parentage certain euphausiid eggs from the English Channel, 

 because of the characters of the larvas hatching therefrom. 



Brook and Hoyle, Sars, and Lebour all agree in describing these eggs (the 

 correct identification of which is made practically certain by cumulative evidence) 

 as inclosed by a perfectly transparent capsule 0.7 to 0.8 millimeter in diameter, the 

 ovum proper having a diameter of approximately 0.3 to 0.4 millimeter. Thus, when 

 first set free in the water they much resemble buoyant fish eggs with wide 

 perivitelline membrane; but cleavage being holoblastic and the development of the 

 nauplius plainly visible within the egg, thanks to its transparency, their crustacean 

 nature is apparent almost from the beginning. Euphausiid eggs are so characteristic 

 in appearance, also, that there is no danger of confusing them with any other buoyant 

 eggs. 



Our own hauls in the Gulf of Maine have yielded considerable numbers of eggs 

 of this same type and size in various stages of development. We first detected them 

 in a surface tow in the Grand Manan Channel, off Campobello Island, August 19, 

 1912 (in the report for that year (Bigelow, 1914, p. 104) they were referred to through 

 error as "balanus" eggs). These were for the most part in early cleavage stages, 

 a few in various stages up to the fully formed nauplius ready to hatch. Eggs of this 

 same type, as well as the recently hatched nauplii, were again taken on the 22d of 

 the month off Penobscot Bay (station 10039). Since that time we have detected 

 similar eggs in the Fundy Deep and off Mount Desert Island in June (stations 10282, 

 10284, and 10286, June 10 to 14, 1915) and off the mouth of the Grand Manan 

 Channel on July 15, 1915 (station 10301). It is not safe to say that all these eggs 

 are Meganyctiphanes, for Lebour (1924) found eggs of Thysanoessa inermis indis- 

 tinguishable from them; but the strong probability that at least part of them belong 



» The considerable series of large adults which I have examined contained none. 



« Metschinkoff (1871, pi. 34, fig. 1) first described the peculiar and very characteristic buoyant eggs of this group of 

 pelagic Crustacea. 



