PLATE X. 



Development o/Sergestid.e (Lucifer). Figures from W. K. Broiiks. 



Note. — The figures on this plate are copied from the original drawings. I am greatly indebted to Dr. Brooks for 

 sending me his drawings and proof of the text of iiis memoir in advance of its appearance in the Philosophical Transactions 

 of the Roj'al Society of London, 1882. The memoir is entitled " LuclJ'cr: a Study in Morphology." 



n'. Supra-tesophageal nerve ganglion. 



c. Compound eye. 



ocl. Simple eye. 



oes. Oisophagus. 



r. Rostrum. 



r e. External branch of appendage. 



ri. Internal branch of appendage. 



&i. Stomach. 



a. Cells which fonii food-yolk, or possibly mnsoblast. 



^. Auditory organ. 



y. Antennal gland. 



&■ Shell gland. 



f. Posterior extremity of abdomen or telson. 



The Roman numerals indicate the appendages of the body in their consecutive order: tlie Arabic numerals denote the 

 somites. In Lucifer the thirteenth somite and its appendages (last thoracic) are not developed in any stage. 



1. Egg undergoing segmentation. There are eiglit segmentation spheres in tlie stage figured. Tlie segmentation 



is regular and total, and a segmentation cavity is formed in the centre of the egg. 



2. Optical section of egg at later stage. One pole has become flattened, and the cell, a, whii/h lies in the centre 



of the flattened area, has its broad end directed toward the segmentation cavity, while the other cells have 

 their broad ends at tlie surface of the egg. Most of the food-yolk has disappeared from the other cell.s, 

 which are now cpiite transparent, while the cell o contains as much food-yolk as ever. 



3. As the segmentation proceeds, the flattened area in fig. 2 becomes a deep pit, and a gastrula results as shown in 



fig. 3. The cell a divides in two and becomes pushed into the segmentation cavity. Whether the two 

 cells a in fig. 3 represent the whole of the cell a in the preceding figure, or whether they are only the inner ends 

 of the same, into which the deutoplasmic elements have withdrawn, and which have then become split off 

 from the outer ends, was not determined. Their further history was not obtained. Brooks inclines to the 

 belief that they represent the inner ends of the cell o in fig. 2, and are not mesoblastic, but go to form a food- 

 yolk like the inner ends of the yolk pyramids in centrolecithal eggs. 



4. Ventral view of embryo artificially removed from the egg thirty hours after oviijosition. I b, labrum. ?n t, 



metastoma. 1, first antenna. II, second antenna. Ill, mandibles. IV, V, VI, buds rejiresenting the two 

 pairs of maxill* and the first pair of maxillipeds of the adult. AVhen the embryo was set free, the body was 

 enveloped in a delicate cuticle, which in the individual figured has been torn ofl' from all the appendages 

 except the first antenna;. 



5. First free nauplius stage, about thirty-six hours after ovijiosition, lateral view. Tiftitr hi. long. The swim- 



ming appendages have become segmented, and the rudiment of the abdomen or telson (J) is apparent. The 

 anus is yet absent, ocl, ocellus. 



6. Second larval stage, or nietanauplius, lateral view. nf^Ti ii^- '°"S' c^', carapace, o e s, cesophagus. 2, intes- 



tine. I, yolk-cells around the stomach {st). n, sub-nesophageal part of nervous cord. 7i', supra-oesophageal 

 nerve ganglion. The anus is now present on the ventral side of the terminal portion of the abdomen. 



7. Third larval stage, or first protozoija stage, raised from the stage represented in fig. 6, dorsal view. tsSh '"• 



from tip of rostrum to base of spines on telson. The hind-body is now about as long as the carapace, 

 and is divided into four somites and a long unsegmented portion («i). Thefour somites (8-11) are those 

 which subsequently bear the third pair of maxillipeds and the three following pairs of legs. A larva w-as taken 

 from the sea agreeing with this one in size and every respect except that the free segments of the hind body 

 were wanting. It is therefore probable that the larva figured is near the end of the first protozoea stage. 

 VII, second maxilliped. r, rostrum, h, heart. The mandibles have become reduced to cutting blades in 

 this stage. 



8. Fourth larval stage, or second protozoea stage, raised from the preceding form, lateral view, yj Ju in. from 



tip of rostrum to fork of telson. o c, rudiment of compound eye. », shell gland opening at the base of the 

 first or second ma.xilla. 



