14 0. E. Beecher — Origin and Significance of Spines. 



conclusive. The proof of its reality will be more clearly 

 shown later on. 



Ontogeny of a Spinose Individual. 



With few exceptions, the embryonic and larval stages of all 

 organisms are devoid of specialized surface features. In other 

 words, they are without ornament and without weapons. The 

 exceptions to this rule seem to be readily explained under the 

 principles of larval adaptations and accelerated development. 

 Cases of the latter kind, therefore, can hardly be considered as 

 exceptions, since they represent, not real larval features, but 

 former adult characters which have been pushed back or which 

 develop earlier so as to appear eventually in the larval or later 

 embryonic stages. In the very earliest stages of embryonic 

 development, the truth of the first statement becomes obvious, 

 and accordingly the protembryonic, mesembryonic, metembry- 

 onic, neoembryonic, and typembryonic stages are without sur- 

 face ornaments or spines. 



Among Mollusca, the protoconch, periconch, and prodisso- 

 conch, or the early larval shells, are smooth and without 

 ornament. Even the prodissoconch of very highly spinose 

 species, as in Spondylus, is as smooth as that of the plainest 

 species of Ostrea, Ano?nia, Avicula, etc. Likewise, the pro- 

 toconch of the most specialized or most retrograde Cephalopod 

 is perfectly plain. In the nepionic stages, the spiny Murex is 

 without spines. In the Brachiopoda, the protegulnm, or early 

 larval shell, is always without sculpture ; while the nauplius of 

 Crustacea and the protaspis of Trilobites are generally spine- 

 less. The young of horned vertebrates are almost universally 

 hornless, the Giraffe being the only mammal born with horns. 

 The very young seedlings of plants are likewise spineless. In 

 insects, the embryonic stages generally have simple cuticles, 

 but in the larval stages of this class and the Crustacea, a great 

 variety of spines and ornamental characters is developed. 

 Altogether, it may be asserted that spines do not appear dur- 

 ing the embryonic stages of animals and plants, and that their 

 initial development is commonly post-larval. 



Examples illustrating the ontogeny of a spinose form could 

 be multiplied indefinitely, and taken from nearly every class of 

 organisms. In all cases, practically the same sequence of 

 events relating to the development of spines would be found. 

 The organism would first be smooth, without sculpture or 

 ornament, like the young of other organisms. At some stage 

 of the ontogeny, the beginnings of spines would appear, and 

 develop first into simple, and later, according to the stage of 

 differentiation attained, into compound spines. This progres- 

 sion would finally reach the maximum, spine growth would 



