MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 341 



After a moult the colors are, as is usual, very bright, and the moulted skin, as it stands intact 

 supported by the an tenure, may easily be mistaken for the living animal. These prawns make no 

 sounds and appear to be very timid. The surface of the whole anterior body and of the large 

 claws is thickly beset with tooth-like spines, the points of which are bent forward, and these 

 may be regarded as an admirable protection against being swallowed head first by an enemy. It 

 is also interesting to notice that the spines of the hinder part of the body project backward, and 

 may thus be of service to Steuopns when attacked from the rear. Their long sensitive an tenure or 

 "feelers" and well-developed eyes doubtless warn them of approaching enemies, which, by their 

 rapid angular movements, they may easily escape. The extraordinary development of the eyes in 

 the older larva? (PI. n) is remarkable. 



The geographical distribution of Stcnopu* Mxpidus is very interesting.* H. Milne-Edwards, 

 in his "Histoire uaturelle desCrustaceV' (:i), gives the habitat of Stenopus hispidm (Latreille) as 

 the "Indian Ocean," following Olivier (1) and the older writers. In the " Kegne Animal" of 

 Cuvier, third edition, "Les Crustace's," p. 137, lie says: "We know of only one species, reported 

 from the Australian seas by Perou and Lesneur." The Samaraug naturalists (5) met with it on 

 the coasts of Borneo and at the Philippines in 1843-'4G. Dana, in 1838-'42, on the Wilkes Expe- 

 dition (6), found it in the South Pacific at the points already noticed. In 1872 E. von Martens (7) 

 describes the species for the first time from the Atlantic, in a collection of Cuban Crustacea made 

 by Dr. J. Gundlach, and de Man in 1888 (9) quotes it from Amboina in his monograph on the 

 Decapoda and Stomatopoda collected in the Indian Archipelago by Dr. J. Brock. 



We can now add to this list the Bahama Islands (Abaco and New Providence). We have 

 also the interesting fact that the larva was taken on our coast at Beaufort, N. C., whither it had 

 probably been carried by the warm waters of the Gulf Stream. We may thfrefore expect to find 

 the adult Steuopus on the Florida Keys, but not much farther north, since this is essentially a 

 tropical form. 



We thus have in Stenopus hispidus another instance of not only the same genus, but also the 

 identical species, occurring on the eastern shores of two continents. It seems not impossible that 

 the prolonged larval period which this animal possesses may have played an important part in its 

 geographical distribution. This may be also true of Oonodactylus chiragra, but on the other hand 

 it can not be asserted of Limulus. In the last case the Asiatic and American forms are specifically 

 distinct. 



II. SEGMENTATION AND EARLY PHASES OF THE EGG. 



The prawn, which hatched her zoe'a brood on the 4th of June, laid eggs the next morning prob- 

 ably at about G o'clock, and as soon as discovered some of these ova were hardened at intervals of 

 a few hours during the next two days. In this way a complete history of the segmentation was 

 obtained. 



First stage. The first eggs preserved (probably 5 to 6 hours after ovulation) are perfectly 

 opaque, nothing but the light-green yolk corpuscles showing through the shell or egg-envelopes. 

 Thin sections prove that the segmentation nucleus has divided, and that its two products lie remote 

 from each other. Physiologically speaking, we now nave two cells, each consisting of a deeply 

 staining nucleus and perinuclear protoplasm. The first segmentation is evidently central. What 

 takes place is briefly as follows : Primitively we have a central nucleus, about which protoplasm 

 is gathered. Around this again is the great mass of yolk, and the whole is encapsuled by the 

 protective chorion and the secondary membrane of attachment. The first division involves only 

 the nucleus and surrounding protoplasm. The products as independent bodies now leave their 

 central position and seek the surface of the egg. In one instance one of these has reached the 

 surface (shown in PI. vi, Fig. 1), while the other is only halfway there on the opposite side. The 

 superficial cell, as seen by the figure, has the same characters as when burie'd in the yolk. In 



* The reason for considering the Bakanian form identical with the Hispidn.s of Olivier, Latreillo, Milne-Edwards, 

 Adams, Dana, and others are given on page 351. 



