V. 



ALPHEUS: A STUDY IN THE DEVELOPMENT OF CRUSTACEA. 



By Francis H. Hereick. 



CONTENTS. 



III. 



IV. 



V. 



VI. 



Introduction. 

 Methods. 

 Part First : 



I. The habits and color variations of Alpbeiis. 

 II. Variations in Alpheus heteroclielis. 



The abbreviated development of Alpheus and its 



relation to the environment. 

 The adult. 



Variations from the specific type. 

 Measurements. 

 VII. The causes and significance of variation in Al- 

 pheus satilcyi. 

 Part Second : 



I. Structure of the first liirva of Alpheus saulci/i. 

 II. The origin of ovarian eggs in Alpheus, Homarus, 

 and Palinurus. 

 III. Segmentation in 4l2)heus minus. 

 IV. The development of Alpheus. 



First slaye: Segmentation to formation of blas- 

 toderm. 

 Second stage: Migration of cells from blastoderm 



to the interior. The invaginatlou-stage. 

 Third singe: Optic disks and ventral plate. 

 Fourth stage: Thickening of optic disks. Ru- 

 diments of appendages. 

 Fifth stage: Rudiments of three pairu of ap- 

 pendages. Optic disks closely united by 

 transverse cord. Degenerative changes. 

 Sixth stage: The egg-uauplius. 

 Seventh stage: Seven jiairs of appendages 

 formed. 



[With thirty 



Part Second— Continued. 



IV. The development of Alpheus — Continued. 



Eighth stage: Nine pairs of appendages present. 



Ninth stage: Eye-2)igment formed. 



Tenth stage: Ganglia of ventral nerve-cord 



distinct and comi)letely separated from the 



skin. 

 Eleventh stage: Embryo about to hatch {Al- 



pheus heterochelis). 

 Twelfth stage: First larva {Alpheus saulcyi). 

 Thirteenth stage: Young Alpheus, four to ten 



days old. 



V. Notes on the Segmentation of Crustacea. 

 VI. Cell Degeneration. 



VII. The Origin aud History of Wandering Cells in 

 Alpheus. 

 VIII. The Development of the Nervous System. 

 IX. The Eyes. 



The median eye of the larva and adult. 

 General anatomy of the eye-stalk. 

 Structure of the ommatidium. 

 Arrangement of the ouiniatidia. 

 The development of the compound eye. 



(1) Origin of the optic disk. 



(2) Development of the retina and the 



optic ganglion. 

 The eye underthe influence of light and dark- 

 ness. 

 X. Summary of Part Second. 

 XI. References. 



Explanation of figures (accompanying each plate), 

 •eight plates.] 



INTRODUCTION. 



The observations ofifered in tbis memoir were uudertaljen at Beaufort, Nortb Carolina, in 

 June, 1885, at the Marine Zoological Station of the Johns Uopkins University. But little was 

 accomplished, however, until the next and following seasons, 1886-87, when I enjoyed the advan- 

 tages of tbis laboratory in the Bahama Islands. 



A part of this memoir was accepted as a thesis for the degree of Ph. D. by the Board of 

 University Studies of the Johns Hopkins University in May, 1888. 



I take this opportunity of thanking Professor Brooks for his invaluable counsel, aid, aud 

 encouragement from the beginning to the end of the work. 



At Nassau, New Providence, during a sojourn of four months (March to July, 1887), I had the 

 rare opportunity of a making a comparative study of a large number of Crustacea. At least thir- 

 teen species of Alpheus were discovered on the coral reefs and shores of New Pro%'idence, and 

 in all these the eggs have been obtained, aud in nearly all the larvte or first zocas have been hatched 

 in aquaria. Many of these forms are new or but little known, and when the means of publication 

 is found it is hoped that their comparative and systematic zoology can be fully illustrated. 



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