TABLE III. 



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



Gastrulation/^ 



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

 excluded) : a, Plant-animals ; h, Worms ; c, Soft-bodied animals (Mollusca) ; 

 d, Star-animals {Echino derma) ; e, Articulates (Arthropoda) ; f, Vertebrates. 



I. 



Total Cleavage, 



Segmentatio totalis. 



Holoblastic Eggs. 



I. Original Cleavage. 



{Segmentatio primordialis.) 

 Archiblastic eggs. 



Bell-gastrula. 



{Archigasti-ula.) 



(Plate I.I. Fig. 1-6.) 



a. Most low Plant-animals (low 

 Sponges, Hydrapolyps, Me- 

 dusa?, Corals). 



6. Many low Worms (Sigitta, 

 Phoronis, Ascidia, many 

 Nematodes, etc.). 



c. A few low Soft-bodied animals 



(Mollusca)— TerehrixtuliX, Ar- 

 giope, Pisidium. 



d. Most Star - animals {Echino- 



derma). 



e. A few low Articulates (some 



Branchiopods, Copepods, Tar- 

 digrades). 

 /. The Skull-less Vertebrate (Am- 

 pliioxus). 



Gastrula with- 

 out 

 nutritive yelk. 

 Uvlogastrula. 



II. Unequal Cleavage. 



(Segmentatio inaiqualis.') 

 Ampbiblastic eggs. 



Hood-gastrula. 



(^Amphigastrula.) 



(Plate II. Fig. 7-17.) 



< 



a. Numerous Plant-animals (many 

 Sponges, Medusa;, Corals, 

 Sipbotiopliores, Ctenophorije). 



h. Most AVorms. 



c. Most Soft-bodied Animals (Mol- 



lusca). 



d. Individual Star-animals (vivi- 



parous species and a lew 

 others). 



e. A few low Articulates (Arthro- 



poda) —both Crustaceans and 

 Tracheates. 

 /. Cyclostoma, Ganoids, Amphibia, 

 Mammals (all r). 



II. 



Partial Cleavaga. 



Segmentatio partialis. 

 Meroblastic eggs. 



Gastrula with 



nutritive yelk. 



Merogastrula. 



HI. Discoidal Cleavage. 



(Segm,entatio discoidalis.) 

 Discoblastic eggs. 



Disc-gastrula. 



( Disco-gas truJa . ) 



(Plate III. Fig. 18-24.) 



IV. Superficial Cleavage, f a. A few Sponges (?) 



(Segmentatio superjicialis .) ''^ 



Periblastic eggs. 



c. Cuttle-fish, or Cephalopods. 



e. Some Articulates (Arthropoda), 

 Millepedes, Scorpions, and 

 others. 



/. Primitive Fishes (Selachii), 

 Osseous Fishes, Reptiles, 

 Birds (and Monotremes i). 



Bladder-gastru' a. 



(Perigastrula.) 

 (Plate III. Fig. 25-aO.) 



Alcyonium (.■■). 



&. Individual Worms (.?). 



e. The great majority of Articu- 

 lates (Artliropoda)—(2v\xs- 

 taccans, Myriopods, Spiders, 

 Insects. 



