TABLE III. 



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

 Gastrnlation. 79 



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

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

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



Total Cleavage. 



Segmentatio totalis. 



Holoblastic Eggs. 



Gastrula with- 

 out 

 nutritive yelk. 



Hologastrula. 



I. Origin al Cleavage. 



(Segmentatio primordialis.) 



Archiblastic eggs. 



Bell-gastrula. 



^Archigastrula.) 



(Plate II. Fig. 1-6.) 



/ a. Most low Plant-animals (low 

 Sponges, Hydrapolyps, Me- 

 dusa?, Corals). 



b. Many low Worms (Sigitta, 



Phoronis, Ascidia, many 

 Nematodes, etc.). 



c. A few low Soft-bodied animals 



(Mollusca)— Terebratula, Ar- 

 giope, Pisidium. 



d. Most Star - animals (Echino- 



derma). 



e. A few low Articulates (some 



Branchiopods, Copepods, Tar- 

 digrades). 

 /. The Skull-less Vertebrate (Am- 

 phioxus). 



II. Unequal Cleavage. 



(Segmentatio inozqualis.) 



Amphiblastic eggs. 



Hood-gastrula. 



(Amphigattrula.} 

 (Plate II. Fig. 7-17.) 



a. Numerous Plant-animals (many 



Sponges, Medusa?, Corals, 

 Siphonophores, Ctenophorae). 



b. Most Worms. 



c. Most Soft-bodied Animals (Mol- 



lusca). 



d. Individual Star-animals (vivi- 



parous species and a few 

 others). 



e. 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. 



Merogastruln. 



I in. Discoidal Cleavage. 



(Segmentatio discoidalis.) 

 Discoblastic eggs. 



Disc-gastrula. 



(Disco-gastrula.) 



(Plate III. Fig. 18-24.) 



c. Cuttle-fish, or Cephalopods. 



e. Some Articulates (Arthropoda), 

 Millepedes, Scorpions, ard 

 others. 



/. Primitive Fishes (Selachit), 

 Osseous Fishes, Reptiles, 

 Birds (and Monotremes .'). 



IV. Superficial Cleavage. 



(Segmentatio superjicialis .) 



Periblasts eggs. 



Bladder-gastru' a. 



(Perigastrula.) 

 (Plate III. Fig. 25-30.) 



f a. A few Sponges (?). 

 Alcyonium (?). 



6. Individual Worms (?) 



e. The great majority of Articu- 

 lates (Arthropoda) — Crus- 

 taceans, Myriopods, Spiders, 

 Insects. 



