INDEX 



683 



Nerve-cord, formation of, in Phascolosoma, 37 7 

 Nerve-ring, formation of, in adult Antedon 



rosacea, 554 ; in Oucumaria planci, 542 

 Nervous system, formation of, in Agelena, 

 226; in embryo (and larva) of Antedon 

 rosacea, 547 ; in Astacus, 184 ; in adult 

 Asterinagibbosa, 477; in larva of Doliolum, 

 637 ; in Donacia, 257, 258 ; in larva of 

 Echinus esculentus, 516 ; in adult Echinus 

 esculentus, 574 ; in Ascidiozooid of Pyro- 

 soma, 640 ; in Cyathozooid of Pyrosoma, 

 634 ; in Salpa, 635 ; in Scolopendra, 282 ; 

 in larva of Synapta digitata, 536 ; in 

 blastozooid of Urochorda, 638 



Neural folds in embryo of Amphioxus 

 lanceolatus, 591 ; in Tornaria larva of 

 Balanoglossus, 578 ; in embryo of Cynthia 

 partita, 619 



Neural groove, formation of, in Donacia, 258 



Neural plate, formation of, in embryo of 

 Amphioxus lanceolatus, 541 ; in Tornaria 

 larva of Balanoglosssus, 578 ; in embryo 

 of Cynthia partita, 614 



Neural tube, formation of, in embryo of 

 Amphioxus lanceolatus, 593 ; in Tornaria 

 larva of Balanoglossus, 578 ; in embryo 

 of Cynthia partita, 619 ; in embryo of 

 Salpa, 636 



Neurenteric canal, formation 6*f, in embryo 

 of Amphioxus lanceolatus, 592 ; in embryo 

 of Cynthia partita, 619 



Neuroblasts of Donacia, 258 ; of Nephelis, 161 



Neuropore, formation of, in embryo of 

 Cynthia partita, 619 ; in larva of Amphi- 

 oxus lanceolatus, 593 ; in larva of Dis- 

 taplia, 632 



Nitschia, 506 ; cultures of, 131 



Notochord, formation of, supposed in Actino- 

 trocha larva, 381, 383 ; in Amphioxus, 592; 

 in larva of Cynthia partita, 614; in New 

 England Tornaria, 579 



Nuclear sap, definition of, 3 



Nucleolus, definition of, 3 



Nucleus of unripe ovum, 3 



Nucula, 349 



Nymphs of Hemimetabola, 287, 288 



Oceania, 59 ; medusae of, 59 

 Ocelli of Dytiscus, 273, 274, 275 

 Octant of egg of Beroe, definition of, 91 

 Ocular plates of Echinus esculentus, 577 

 Odonata, 245, 272, 277, 286 ; embryonic 



development of, 266 



Oesophagus, formation of, in Agelena, 235 ; 

 in Antedon rosacea, 550 ; in Astacus, 

 183 ; in larva of Asterias, 462 ; in larva 

 of Balanoglossus davigerus, 573 ; in larva 

 of Ophiothrix fragilis, 487 ; in larva of 

 Synapta digitata, 532 ; in Terebrati(lina 

 septentrionalis, 411 



Olfactory organ of Sagitta lipunctata, for- 

 mation of, 434 



Oligochaeta, 1 28, 600 ; development of, 

 156-159 



Ommatidium, formation of, in compound eye 



of Astacus, 189 ; in compound eye of 



Dytiscus, 276 ; in lateral eyes of Limv.lus, 



237 



Onychophora, 169, 206, 285 ; development 



of, 170-176 



Oocyte of first order, 9 ; definition of, 3 

 Oocyte of second order, 9 

 Oogeuesis, definition of, 2 

 Oogonium, definition of, 3 

 Oostegites of Entoniscidae, 219 

 Oozooid of Botryllidae, 642 ; of Salpa, 640 

 Open larva of Patella, formation of, 307 

 Operculum of Patella, formation of, 303 

 Ophiopluteus larva, 498, 508, 509, 521, 

 529, 532, 533, 565, 654 ; compared with 

 Bipinnaria larva, 491, 492 ; compared with 

 Echinopluteus larva, 51 1 ; definition of, 490 

 Ophiothrix fragilis, 484, 501, 503, 504, 507, 

 508, 514, 529; abnormal development of, 

 502 ; development of, 485-498 

 Ophiura, larva of, 489 

 Ophiura brevispina, 484 ; development of, 



501-503 



Ophiuroidea, 287, 461, 464, 456, 508, 

 514, 515, 522, 523, 530, 531, 534, 536, 

 538, 541, 542, 543, 560, 564, 565 ; de- 

 velopment of, 484-504 

 Opisthobrauchiata, 280, 281, 291, 320, 324 

 Optic ganglion, formation of, in Astacus, 184 

 Oral coelom, formation of, in Antedon 



rosacea, 552 



Oral cone of Amelia, 69 

 Oral lobe of larva of Echinus esculentus, 509 

 Oral ring of plates, formation of, in larva of 



Antedon rosacea, 547 



Oral tentacles of Tubular ia, development of, 56 

 Organ-forming substances, 658, 659 ; in egg 

 of Cynthia, 631 ; in egg of Dentalium, 

 330-332 ; in egg of Paludina, 309 

 Organogeny, definition of, 27 

 Orientation, methods of, 34 

 Orthoptera, 201, 245, 272, 277, 278, 286, 288 

 Oscarella, 43, 44, 51 ; metamorphosis of, 44 

 Osmic acid (Osmium tetroxide), definition of, 



32 ; use of, 32 



Ostium, formation of, in larva of Aurelia, 71 

 Ostium of heart, development of, in Agelena, 



229 



Ostracoda, 177, 185 ; ancestral origin of, 212 

 Ostrea, brephic stage of, 22 

 Ostrea virginiana, veliger larva of, 348 

 Otocysts, formation of, in Dentalium, 329 ; 

 in Dreissensia, 342 ; in Loligo, 358 ; in 

 Paludina, 315 ; in Patella, 301 ; in 

 Synapta digitata, 539 



Ovary of Ascaris megalocephala, 438 ; 

 development of, in Julus, 284 ; of 

 Molgula, 628 ; of Phyllodromia, 263 

 Oviduct, formation of, in Ascaris megalo- 

 cephula, 438 ; in Molgula, 628, 629 ; in 

 Phyllodrmnia, 263 ; in Sagitta bipunctata, 

 454 

 Ovum (a) definition of, 2 



