V. 



ALPHEUS: A STUDY IN THE DEVELOPMENT OF CRUSTACEA. 



By FRANCIS H. HERRICK. 



CONTENTS. 



Introduction. 

 Methods. 

 PART FIRST : 



I. The habits and color variations of Alpheus. 

 II. Variations in Alpheus heterochelis. 

 III. The abbreviated development of Alpheus and its 



relation to the environment. 

 IV. The adult. 



V. Variations from the specific type. 

 VI. Measurements. 

 VII. The causes and significance of variation in .11- 



pheus saulcyi. 

 PART SECOND : 



I. Structure of the first larva of Alpln-ns sanlcyi. 

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



and Palinurus. 



III. Segmentation in llpheus minim. 

 IV. The development of Alpheus. 



First stage: Segmentation to formation of blas- 

 toderm. 

 Second stage: Migration ofcells from blastoderm 



to the interior. The iuvagination stage. 

 Third sta/je: Optic disks and ventral plate. 

 Fourth stage: Thickening of optic disks. Ku- 



dimeuts of appendages. 



Fifth stage: Rudiments of three pairs) of ap- 

 pendages. Optic disks closely united by 

 transverse cord. Degenerative changes. 

 Sixth stage: The egg-naupliua. 

 Seventh stage: Seven pairs of appendages 

 formed. 



[With thirty 



PART SECOND Continued. 



IV. The development of Alpheus Continued. 



Eighth stage: Nine pairs of appendages present. 

 \intli stage: Eye-pigment formed. 

 Tenth stage: Ganglia of ventral nerve-cord 

 distinct and completely separated from the 

 skin. 



Klerenlh stage: Embryo about to batch (Al- 

 pheus heterochelis'). 



TiettJ'lh xlage: First larva (Alpheus saulcyi). 

 Thirteenth xla<i< : Young Alphi-us, four to ten 



days old. 



V. Notes on the Segmentation of Crustacea. 

 VI. Cell Degeneration. 

 VII. The Origin and History of Wandering Cells in 



Alphvus. 



VIII. The Development of the Nervous System. 

 IX. The E.\r. 



The median eye of the larva and adult. 

 General anatomy of the eye-stalk. 

 Structure of the onimatidium. 

 Arrangement of the ommatidiu. 

 The development of the compound eye. 

 (1} Origin of the optic disk, 

 ('.i) Development of the retina and the 



optic ganglion. 



The eye under the influence of light and dark- 

 ness. 



X. Summary of Part Second. 

 XI. References. 



Explanation of figures (accompanying each plate). 

 eight plates.] 



INTRODUCTION. " 



The observations offered in this memoir were undertaken at Beaufort, North Carolina, in 

 Juue, 1885, at the Marine Zoological Station of the Johns Hopkins University. But little was 

 accomplished, however, until the next and following seasons, 188G-'87, when I enjoyed the advan- 

 tages of this 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, and 

 encouragement from the beginning to the end of the work. 



At Nassau, New Providence, during a sojourn of four mouths (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 Providence, and 

 in all these the eggs have been obtained, and in nearly all the larvre or first zoeas 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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