TABLE III. 



List of the most important differences in Animal Egg-cleavage and 



Gastrulation. 7 ' 



The letters a-/ indicate the 6 animal tribes (the primitive animals being 

 excluded) : a, Plant-animals ; b, Worms ; c, Soft-bodied animals (MolVussa) ; 

 i, Star-animals {Echinoderma) ; e, Articulates (Arthropoda) ; /, Vertebrates. 



I. 



Total Cleavage. 



Segmmtatio totalis. 

 Hoioblastic Eggs. 



Oafrtrula with- 

 out 

 nutritive yelk. 



Hologastrula. 



I. Original Cleavage. 

 (Segmentatio primordialis, 



Arcbiblastic eggs. 



Bell-gas trula. 



v Archigastrula .) 



(Plate II. Fig. 1-6.) 



) 



a. Most low Plant-animals (low 

 Sponges, Hydrapolyps, Me- 

 dusae, Corals). 



6. Many low Worms (Sagitta, 

 Phoronis, Ascidia, many 

 Nematodes, etc.). 



c. A few low Soft-bodied animals 



(Mbllusca) — Terebratula, Ar- 

 giope, Pisidium. 



d. Most Star - animals (Echino- 



derma). 



e. A few low Articulates (some 



Brancbiopods, Copepods, Tar- 

 digrades). 

 /. The Skull-less Vertebrate (Am- 

 phioxus). 



n. Unequal Cleavage. 



(Segmentatio inaqualis.) 

 Ampbiblastic eggs. 



Hood-gastrula. 



(Amphigattrvla.') 



(Plate II. Fig. t-17.) 



a. Numerous Plant-animals (many 



Sponges, Medusae, Corals, 

 Siphonophores, Ctenophorae). 



b. Most Worms. 



c. Most Soft-bodied Animals (MoU 



lusca). 



d. Individual Star-animals (vivi- 



parous species and a few 

 others). 



c. A few low Articulates (Arthro- 

 poda) -both Crustaceans and 

 Tracheates. 



/. Cyclostoma, Ganoids, Amphibia, 

 Mammals (all ?). 



n. 



Partial Cleavage. 



Segmentatio partialis. 



Meroblastic eggs. 



Gastrula with 



nutritive yelk. 



Mercgastrula. 



m. Discoidal Cleavage. 



(Segmentatio discoidalis.) 



Discoblastic eggs. 



Disc-gastrula. 



(Disco-gastrula.) 



(Plate III. Fig. 18-24.) 



e. Cuttle-fish, or Cephalopods. 



e. Some Articulates (Arthropoda}, 

 Millepedes, Scorpions, ard 

 others. 



/. Primitive Fishes (Selachii), 

 Osseous Fishes, Reptiles, 

 Birds (and Monotremes ?). 



IV. Superficial Cleavage. / a. A few Sponges (?). 

 (Segmentatio super [facialis .) 

 Periblasts eggs. 



Alcyonium (?). 

 6. Individual Worms (?) 



Bladder-gastru 1 a. 



(Perigastrula.) 

 (Plate III. Fig. 26-30.) 



«. The great majority of Articu- 

 lates (Arthropoda)— Crus- 

 taceans, Myriopocto, Spiders, 

 Insects. 



